Working machine

ABSTRACT

A working machine includes a controller to perform automatic deceleration to automatically reduce a first rotation speed of a left traveling motor to output a power to a left traveling device on a left portion of a machine body and a second rotation speed of a right traveling motor to output a power to a right traveling device on a right portion of the machine body by shifting a speed stage of each of the left and right traveling motors from a second speed to a first speed that is lower than the second speed. The controller is configured or programmed to determine, based on the second rotation speed, a left threshold for judging whether to perform the automatic deceleration in left pivot turn of the machine body, and to determine, based on the first rotation speed, a right threshold for judging whether to perform the automatic deceleration in right pivot turn of the machine body.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese PatentApplication No. 2020-137169 filed on Aug. 15, 2020 and to JapanesePatent Application No. 2021-45017 filed on Mar. 18, 2021. The entirecontents of this application are hereby incorporated herein byreference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a working machine such as a skid steerloader, a compact track loader, and a backhoe.

2. Description of the Related Art

Japanese unexamined patent application publication No. 2017-179923discloses a technique for decelerating and accelerating a workingmachine. The working machine described in Japanese unexamined patentapplication publication No. 2017-179923 has a prime mover including anengine, a hydraulic pump configured to be operated by power of the primemover and to output an operation fluid, a traveling hydraulic deviceconfigured to switch a speed between a first speed and a second speedthat is faster than the first speed according to a pressure of theoperation fluid, an operation valve configured to change the pressure ofthe operation fluid applied to the traveling hydraulic device, and ameasurement device configured to detect the pressure of the operationfluid. When a detected pressure, which is a pressure of the operationfluid detected by the measurement device, drops from a set pressurecorresponding to the second speed to a predetermined pressure or lower,the operation valve reduces the pressure of the operation fluid appliedto the traveling hydraulic device to decelerate the traveling hydraulicdevice to the first speed.

SUMMARY OF THE INVENTION

The working machine of Japanese unexamined patent applicationpublication No. 2017-179923 is capable of automatically deceleratingfrom a second speed to a first speed when a pressure of an operationfluid in traveling to be supplied to a traveling device is equal to orhigher than a predetermined pressure. However, due to a traveling state(that is, spin turn, pivot turn, straight traveling) of the workingmachine (that is, a traveling device), the deceleration may be causedunexpectedly.

The present invention is provided to solve the above-mentioned problemsof the conventional technique, and is intended to provide a workingmachine capable of smoothly decelerating according to the travelingstate of the working machine.

Technical means of the present invention for solving this technicalproblem is characterized by the following points.

A working machine includes a machine body, a left traveling devicelocated left on the machine body, a right traveling device located righton the machine body, a left traveling motor to output a power to theleft traveling device, a right traveling motor to output a power to theright traveling device, a first rotation detector to detect a firstrotation speed that is a rotation speed of the left traveling motor, asecond rotation detector to detect a second rotation speed that is arotation speed of the right traveling motor, a left traveling pump tosupply operation fluid to the left traveling motor, a right travelingpump to supply operation fluid to the right traveling motor, a travelingoperation device to operate at least one of the left traveling pump andthe right traveling pump, and a controller configured or programmed toperform automatic deceleration to automatically reduce the firstrotation speed and the second rotation speed by shifting a speed stageof each of the left and right traveling motors from a second speed stageto a first speed stage that is lower than the second speed. Thecontroller is configured or programmed to determine, based on the secondrotation speed, a left threshold for judging whether to perform theautomatic deceleration in left pivot turn of the machine body, and todetermine, based on the first rotation speed, a right threshold forjudging whether to perform the automatic deceleration in right pivotturn of the machine body.

The controller is configured or programmed to determine the leftthreshold to be lower as the second rotation speed decrease, todetermine the left threshold to be higher as the second rotation speedincreases, to determine the right threshold to be lower as the firstrotation speed decreases, and to determine the right threshold to behigher as the first rotation speed increases.

The working machine includes a first circulation fluid line connectingthe left traveling pump to the left traveling motor, a secondcirculation fluid line connecting the right traveling pump to the righttraveling motor, a first pressure detector provided on a portion of thefirst circulation fluid line connected to a first port of the lefttraveling motor and configured to detect a first traveling pressure thatis a pressure of operation fluid flowing in the portion of the firstcirculation fluid line connected to the first port during rotation ofthe left traveling motor, a second pressure detector provided on aportion of the first circulation fluid line connected to a second portof the left traveling motor and configured to detect a second travelingpressure that is a pressure of operation fluid flowing in the portion ofthe first circulation fluid line connected to the second port duringrotation of the left traveling motor, a third pressure detector providedon a portion of the second circulation fluid line connected to a thirdport of the right traveling motor and configured to detect a thirdtraveling pressure that is a pressure of operation fluid flowing in theportion of the second circulation fluid line connected to the third portduring rotation of the right traveling motor, a fourth pressure detectorprovided on a portion of the second circulation fluid line connected toa fourth port of the right traveling motor and configured to detect afourth traveling pressure that is a pressure of operation fluid flowingin the portion of the second circulation fluid line connected to thefourth port during rotation of the right traveling motor. The controlleris configured or programmed to perform the automatic deceleration duringleft pivot turn of the machine body when the third traveling pressure orthe fourth traveling pressure is equal to or higher than the leftthreshold and to perform the automatic deceleration during right pivotturn of the machine body when the first traveling pressure or the secondtraveling pressure is equal to or higher than the right threshold.

The controller is configured or programmed to perform the automaticdeceleration during left pivot turn of the machine body when a thirddifferential pressure obtained by subtracting the fourth travelingpressure from the third traveling pressure or a fourth differentialpressure obtained by subtracting the third traveling pressure from thefourth traveling pressure is equal to or higher than the left threshold,and to perform the automatic deceleration during right pivot turn of themachine body when a first differential pressure obtained by subtractingthe second traveling pressure from the first traveling pressure or asecond differential pressure obtained by subtracting the first travelingpressure from the second traveling pressure is equal to or higher thanthe right threshold.

The controller is configured or programmed to change the left thresholdand the right threshold according to variation in a revolving speed of aprime mover.

The controller is configured or programmed to determine the leftthreshold when the traveling operation device is operated in a directioncorresponding to the left pivot turn of the machine body, and todetermine the right threshold when the traveling operation device isoperated in a direction corresponding to the right pivot turn of themachine body.

The controller is configured or programmed to determine, according to afaster one of the first rotation speed and the second rotation speed, aspin-turn threshold for judging whether to perform the automaticdeceleration during spin turn of the machine body.

The controller is configured or programmed to determine a spin-turnthreshold for judging whether to perform the automatic decelerationduring spin turn of the machine body so that the spin turn threshold islower than the left threshold and the right threshold.

The controller is configured or programmed to perform the automaticdeceleration during spin turn of the machine body when any one of thefirst traveling pressure, the second traveling pressure, the thirdtraveling pressure, and the fourth traveling pressure is equal to orhigher than the spin-turn threshold.

The controller is configured or programmed to perform the automaticdeceleration when the traveling operation device is operated in adirection corresponding to spin turn and any one of the first travelingpressure, the second traveling pressure, the third traveling pressure,and the fourth traveling pressure is equal to or higher than thespin-turn threshold.

The controller is configured or programmed to perform the automaticdeceleration during spin turn of the machine body when an one of a firstdifferential pressure obtained by subtracting the second travelingpressure from the first traveling pressure, a second differentialpressure obtained by subtracting the first traveling pressure from thesecond traveling pressure, a third differential pressure obtained bysubtracting the fourth traveling pressure from the third travelingpressure, and a fourth differential pressure obtained by subtracting thethird traveling pressure from the fourth traveling pressure is equal toor higher than the spin-turn threshold.

According to the present invention, deceleration can be performedsmoothly according to a traveling state of the working machine.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of preferred embodiments of the presentinvention and many of the attendant advantages thereof will be readilyobtained as the same becomes better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings described below.

FIG. 1 is a view showing a hydraulic system (a hydraulic circuit) forworking machine.

FIG. 2 is a view showing an operational direction of a travelingoperation member.

FIG. 3 is a view showing a relationship between a second rotation speedLM_(RPM), a first left threshold ST1 _(L), a second left threshold ST2_(L).

FIG. 4 is a view showing a relationship between a first rotation speedLM_(RPM), a first right threshold ST1 _(R), a second right threshold ST2_(R).

FIG. 5 is a view showing a relationship between a rotation differenceΔMP, a first straight threshold SF1 _(S), and a second straightthreshold SF2 _(S).

FIG. 6A is a view showing a relationship between a rotation-ratiodifference ΔDP, and the straight thresholds SF1 _(S) and SF2 _(S).

FIG. 6B is a view showing a relationship between a rotation ratio ΔDQ,and the straight thresholds SF1 _(S) and SF2 _(S).

FIG. 7 is a view showing a relationship between the first rotation speedLM_(RPM), a second rotation speed RM_(RPM), the first straight thresholdSF1 _(S), the second straight threshold SF2 _(S).

FIG. 8A is a view showing a modified example of a traveling operationdevice.

FIG. 8B is a view showing a modified example of another travelingoperation device.

FIG. 9 is a side view showing a track loader that is an example of aworking machine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments will now be described with reference to theaccompanying drawings, wherein like reference numerals designatecorresponding or identical elements throughout the various drawings. Thedrawings are to be viewed in an orientation in which the referencenumerals are viewed correctly.

With reference to drawings as appropriate, a preferred embodiment of ahydraulic system for a working machine and the working machine havingthe hydraulic system will be described below.

FIG. 9 shows a side view of a working machine of the present invention.FIG. 9 shows a compact track loader as an example of the workingmachine. However, the working machine of the present invention is notlimited to the compact track loader, but may be other types of loaderworking machines, such as a skid steer loader, for example. In addition,the working machine may be a working machine other than the loaderworking machine.

As shown in FIG. 9, a working machine 1 has a machine body 2, a cabin 3,a working device 4, and a pair of traveling devices 5L and 5R. In theembodiment of the present invention, a forward direction of a driversiting on a driver seat 8 of the working machine 1 (a left side in FIG.9) is referred to as the front, a rearward direction of the driver (aright side in FIG. 9) is referred to as the rear, a leftward directionof the driver (a front surface side of FIG. 9) is referred to as theleft, and a rightward direction of the driver (a back surface side ofFIG. 9) is referred to as the right. A horizontal direction, which isorthogonal to a fore-and-aft direction, is referred to as a machinewidth direction. A direction from the center of the machine body 2 tothe right or left is referred to as a machine outward direction. Inother words, the machine outward direction is the machine widthdirection and separates away from the machine body 2. A directionopposite to the machine outward direction is referred to as a machineinward direction. In other words, the machine inward direction is themachine width direction and approaches the machine body 2.

The cabin 3 is mounted on the machine body 2. The cabin 3 incorporatesthe driver seat 8. The working device 4 is attached to the machine body2. A pair of traveling devices 5L and 5R are arranged on the outside ofthe machine body 2. A prime mover 32 is mounted inside a rear portion ofthe machine body 2.

The working device 4 has booms 10, a working tool 11, lift links 12,control links 13, boom cylinders 14, and bucket cylinders 15.

The booms 10 are arranged on right and left sides of the cabin 3 andpivotable up and down. The working tool 11 is, for example, a bucket.The bucket 11 is arranged at tip portions (that is, front end portions)of the booms 10 to be movable up and down. The lift links 12 and thecontrol links 13 support a base portion (that is, a rear portion) of theboom 10 so that the boom 10 can be swung up and down. The boom cylinders14 are extended and contracted to lift and lower the boom 10. The bucketcylinders 15 are extended and contracted to swing the bucket 11 up anddown.

Front portions of the right and left booms 10 are connected to eachother by a deformed connecting pipe. Base portions (that is, rearportions) of the booms 10 are connected to each other by a circularconnecting pipe.

The pair of lift links 12, the pair of control links 13, and the pair ofboom cylinders 14 are arranged right and left on the machine body 2,corresponding to the right and left booms 10.

The lift links 12 are extended vertically from rear portions of the baseportions of the booms 10. Upper portions (that is, one ends) of the liftlinks 12 are pivotally joined to the rear portions of the base portionsof the booms 10 via respective pivot shafts (referred to as first pivotshafts) 16 rotatably around lateral axes defined by the pivot shafts 16relative to the rear portions of the base portions of the booms 10.Lower portions (that is, the other ends) of the lift links 12 arepivotally joined to the rear portion of the machine body 2 viarespective pivot shafts (referred to as second pivot shafts) 17rotatably around the lateral axes defined by the pivot shafts 17relative to the rear portion of the machine body 2. The second pivotshafts 17 are located below the first pivot shafts 16.

Upper portions of the boom cylinders 14 are pivoted on respective pivotshafts (referred to as third pivot shafts) 18 rotatably around lateralaxes defined by the pivot shafts 18. The third pivot shafts 18 areprovided at the base portions of the booms 10, especially, at frontportions of the base portions. Lower portions of the boom cylinders 14are pivoted on respective pivot shafts 19 rotatably around lateral axesdefined by the pivot shafts 19. The fourth pivot shafts 19 are locatedat a lower portion of the rear portion of the machine body 2 and belowthe third pivot shafts 18.

The control links 13 are located in front of the lift links 12. One endsof the control links 13 are pivoted on respective pivot shafts (referredto as fifth pivot shafts) 20 rotatably around lateral axes defined bythe pivot shafts 20. The fifth pivot shafts 20 are located, in themachine body 2, on positions forward of the lift links 12. The otherends of the control links 13 are pivoted on respective pivot shafts(referred to as sixth pivot shafts) 21 rotatably around lateral axesdefined by the pivot shafts 21. The sixth pivot shafts 21 are located,in the boom 10, forward of and above the second pivot shafts 17.

By extending and contracting the boom cylinders 14, the booms 10 areswung up and down around the first pivot shafts 16 with the baseportions of the booms 10 supported by the lift links 12 and the controllinks 13, thereby lifting and lowering the tip end portions of the booms10. The control links 13 are swung up and down around the fifth pivotshafts 20 by the vertical swinging of the booms 10. The lift links 12are swung back and forth around the second pivot shafts 17 by thevertical swinging of the control links 13.

An alternative working tool instead of the bucket 11 can be attached tothe front portions of the booms 10. For example, an attachment (that is,an auxiliary attachment) such as a hydraulic crusher, a hydraulicbreaker, an angle broom, an earth auger, a pallet fork, a sweeper, amower, a snow blower, or the like may serve as the alternative workingtool.

A connector member 50 is located at the front portion of the left boom10. The connector member 50 is a device configured to connect ahydraulic equipment attached to the auxiliary attachment to a firstpiping member such as a pipe located on the left boom 10. Specifically,the first piping member can be connected to one end of the connectormember 50, and a second piping member connected to the hydraulicequipment of the auxiliary attachment can be connected to the other end.In this manner, an operation fluid flowing in the first piping memberpasses through the second piping member and is supplied to the hydraulicequipment.

The bucket cylinders 15 are located respectively near the front portionsof the booms 10. The bucket cylinders 15 are extended and contracted toswing the bucket 11.

The traveling device 5L is located left on the machine body 2, and thetraveling device 5R is located right on the machine body 2. In theembodiment, a crawler type (including a semi-crawler type) travelingdevice is adopted for the pair of traveling devices 5L and 5R. Awheel-type traveling device having front wheels and rear wheels may alsobe adopted. For convenience of explanation, the traveling device 5L maybe referred to as the left traveling device 5L, and the traveling device5R may be referred to as the right traveling device 5R.

The prime mover 32 is an internal combustion engine such as a dieselengine, gasoline engine, an electric motor, or the like. In theembodiment, the prime mover 32 is the diesel engine, but is not limitedthereto.

The hydraulic system for the working machine 1 will be described below.

As shown in FIG. 1, the hydraulic system for the working machine 1 has afirst hydraulic pump P1 and a second hydraulic pump P2. The firsthydraulic pump P1 is a pump to be driven by power of the prime mover 32(see FIG. 9) and includes a constant displacement gear pump. The firsthydraulic pump P1 is capable of delivering operation fluid stored in atank 22. Specifically, the first hydraulic pump P1 discharges operationfluid that is mainly used for control. For convenience of explanation,the tank 22 that stores operation fluid may be referred to as anoperation fluid tank. Of the operation fluid delivered from the firsthydraulic pump P1, the operation fluid used for control is referred toas pilot fluid, and a pressure of the pilot fluid is referred to as apilot pressure.

The second hydraulic pump P2 is a pump to be driven by the power ofprime mover 32, and includes a constant displacement gear pump. Thesecond hydraulic pump P2 is capable of delivering operation fluid storedin the tank 22 and, for example, supplies the operation fluid to fluidlines of a working system. For example, the second hydraulic pump P2supplies operation fluid to control valves (that is, flow-rate controlvalves) that control the boom cylinders 14 for operating the booms 10,the bucket cylinders 15 for operating the bucket, and an auxiliaryhydraulic actuator for operating the auxiliary hydraulic actuator.

The hydraulic system for the working machine 1 has a pair of travelingmotors 36L and 36R and a pair of traveling pumps 53L and 53R. The pairof traveling motors 36L and 36R output power transmitted to the pair oftraveling devices 5L and 5R. The traveling motor 36L transmitsrotational power to the traveling device (referred to as a lefttraveling device) 5L, and the traveling motor 36R transmits rotationalpower to the traveling device (referred to as a right traveling device)5R.

The pair of traveling pumps 53L and 53R are pumps to be driven by powerof the prime mover 32 and are, for example, swash plate typed variabledisplacement axial pumps. The traveling pumps 53L and 53R are driven todeliver operation fluid supplied to the respective traveling motors 36Land 36R. The traveling pump 53L supplies the operation fluid to thetraveling motor 36L, and the traveling pump 53R supplies the operationfluid to the traveling motor 36R.

For convenience of explanation, the traveling pump 53L may be referredto as a left traveling pump 53L, the traveling pump 53R may be referredto as a right traveling pump 53R, the traveling motor 36L may bereferred to as a left traveling motor 36L, and the traveling motor 36Rmay be referred to as a right traveling motor 36R.

Each of the left traveling pump 53L and the right traveling pump 53R hasa pressure receiver portion 53 a and a pressure receiver portion 53 b towhich a pressure (that is, a pilot pressure) of the operation fluid(that is, pilot fluid) from the first hydraulic pump P1 is applied, andangles of the swash plates are changed by the pilot pressures applied tothe pressure receiver portions 53A and 53B. By changing the angle ofeach of the swash plates, the operation fluid delivery amount (that is,delivery flow rate) and direction of each of the left traveling pump 53Land the right traveling pump 53R is changed.

The left traveling pump 53L and the left traveling motor 36L areconnected by a connecting fluid line 57 h (referred to as a firstcirculation fluid line), and operation fluid delivered from the lefttraveling pump 53L is supplied to the left traveling motor 36L. Theright traveling pump 53R and the right traveling motor 36R are connectedby a connecting fluid line 57 i (referred to as a second circulationfluid line), and the operation fluid delivered from the right travelingpump 53R is supplied to the right traveling motor 36R.

The left traveling motor 36L is rotated by the operation fluid deliveredfrom the left traveling pump 53L. By changing a flow rate of operationfluid to the left traveling motor 36L, a rotation speed (that is, arevolving speed) of the left traveling motor 36L can be changed. A swashplate switching cylinder 37L is connected to the left traveling motor36L. By extending and contracting the swash plate switching cylinder 37Lin one direction or the other direction, a rotation speed of the lefttraveling motor 36L can be changed. That is, when the swash plateswitching cylinder 37L is contracted, the rotation speed of the lefttraveling motor 36L is set so as to correspond to a first speed(referred to as a predetermined low speed range), which is a slowerspeed position. When the swash plate switching cylinder 37L is extended,a rotation speed of the left traveling motor 36L is set so as tocorrespond to a second speed (referred to as a predetermined high speedrange), which is a faster speed position. That is, a rotation speed ofthe left traveling motor 36L is shiftable between the first speed andthe second speed.

The right traveling motor 36R is rotated by the operation fluiddelivered from the right traveling pump 53R. By changing a flow rate ofoperation fluid to the right traveling motor 36R, a rotation speed ofthe right traveling motor 36R can be changed. A swash plate switchingcylinder 37R is connected to the right traveling motor 36R. By extendingand contracting the swash plate switching cylinder 37R in one directionor the other direction, a rotation speed of the right traveling motor36R can be changed. That is, when the swash plate switching cylinder 37Ris contracted, a speed stage of rotation speed of the right travelingmotor 36R is set to a first speed (referred to as a predetermined lowspeed range), which is a slower speed stage. When the swash plateswitching cylinder 37R is extended, a speed stage of rotation speed ofthe right traveling motor 36R is set to a second speed (referred to as apredetermined high speed range), which is a faster speed stage. That is,a rotation speed of the right traveling motor 36R is shiftable betweenthe first speed and the second speed.

As shown in FIG. 1, the hydraulic system for the working machine 1 has atraveling switching valve 34. The traveling switching valve 34 isconfigured to change rotation speeds of the traveling motors 36L and 36R(that is, the left traveling motor 36L and the right traveling motor36R) by shifting the rotation speed of each of the left and righttraveling motors 36L and 36R between the first speed and the secondspeed. A state of the traveling switching valve 34 setting the rotationspeed stage of each of the left and right traveling motors 36L and 36Rto the first speed stage is referred to as a first state of thetraveling switching valve 34, and a state of the traveling switchingvalve 34 setting the rotation speed stage of each of the left and righttraveling motors 36L and 36R to the second speed stage is referred to asa second state of the traveling switching valve 34. The travel switchingvalve 34 includes first switching valves 71L and 71R and a secondswitching valve 72.

The first switching valve 71L is connected via a fluid line to the swashplate switching cylinder 37L of the left traveling motor 36L, andincludes a two-position switching valve shiftable between a firstposition 71L1 and a second position 71L2. The first switching valve 71Lset at the first position 71L1 contracts the swash plate switchingcylinder 37L, and the first switching valve 72L set at the secondposition 71L2 extends the swash plate switching cylinder 37L.

The first switching valve 71R is connected via a fluid line to the swashplate switching cylinder 37R of the right traveling motor 36R, andincludes a two-position switching valve shiftable between a firstposition 71R1 and a second position 71R2. The first switching valve 71Rset at the first position 71R1 contracts the swash plate switchingcylinder 37R, and the first switching valve 71R set at the secondposition 71R2 extends the swash plate switching cylinder 37R.

The second switching valve 72 is a solenoid valve for shifting the firstswitching valve 71L and the first switching valve 71R, and is configuredas a two-position switching valve shiftable between a first position 72a and a second position 72 b. The second switching valve 72 is connectedto the first switching valve 71L and the first switching valve 71R by afluid line 41. The second switching valve 72 set at the first position72 a switches the first switching valve 71L and the first switchingvalve 71R to the first positions 71L1 and 71R1, and the second switchingvalve 72 set at the second position 72 b switches the first switchingvalve 71L and the first switching valve 71R to the second positions 71L2and 71R2.

The traveling switching valve 34 is set in the first state to contractthe swash plate switching cylinders 37L and 37R and to shift rotationspeeds of the traveling motors 36L and 36R to the first speed when thesecond switching valve 72 is set at the first position 72 a, the firstswitching valve 71L is set at the first position 71L1, and the firstswitching valve 71R is set at the first position 71R1. The travelingswitching valve 34 is set in the second state to extend the swash plateswitching cylinders 37L and 37R and to shift rotation speeds of thetraveling motors 36L and 36R to the second speed when the secondswitching valve 72 is set at the second position 72 b, the firstswitching valve 71L is set at the second position 71L2, and the firstswitching valve 71R is set at the second position 71R2. Accordingly, thetraveling switching valve 34 allows the traveling motors 36L and 36R tohave a common rotation speed stage shiftable between the first speed andthe second speed.

An operation device (that is, a traveling operating device) 54 isconfigured to apply a part of the operation fluid to the pressurereceiver portions 53 a and 53 b of each of the traveling pumps 53L and53R (that is, the left traveling pump 53L and the right traveling pump53R) when a traveling operation member 59 is operated, thereby changingthe angles of swash plates (referred to as swash plate angles) of thetraveling pumps 53L and 53R. The operation device 54 includes thetraveling operation member 59 and a plurality of operation valves 55.

The traveling operation member 59 is an operation lever that issupported by the operation valves 55 and swings in a lateral direction(that is, the machine width direction) or the fore- and -aft direction.The traveling operation member 59 is operable to turn to the right andto the left from a neutral position N, and to turn to the front and tothe rear from the neutral position N. In other words, the travelingoperation member 59 is swingable in at least four directions from theneutral position N. For convenience of explanation, the forward andbackward directions, that is, the fore-and-aft direction, may bereferred to as a first direction. The rightward and leftward directions,that is, the lateral direction (that is, the machine width direction),are may be referred to as a second direction.

The plurality of operation valves 55 are operated by the common singletraveling operation member 59. The plurality of operation valves 55 areoperated based on swinging of the traveling operation member 59. Anoutput fluid line 40 is connected to the plurality of operation valves55, and the part of operation fluid (that is, pilot fluid) from thefirst hydraulic pump P1 can be supplied to the operation valves 55through the output fluid line 40. The plurality of operation valves 55include an operation valve 55A, an operation valve 55B, an operationvalve 55C, and an operation valve 55D.

When the traveling operation member 59 is swung forward, i.e., in one ofopposite fore-and-aft directions (one of opposite first directions) fromthe neutral position, or, when a forward directional operation ofperformed, the operation valve 55A changes a pressure of operation fluidoutput therefrom according to an operation amount of the forwarddirectional operation. When the traveling operation member 59 is swungbackward, i.e., in the other of the opposite fore-and-aft directions(that is, in the other of the opposite first directions, or when abackward directional operation of performed, the operation valve 55Bchanges a pressure of operation fluid output therefrom according to anoperation amount of the backward directional operation. When thetraveling operation member 59 is swung rightward, i.e., in one of theopposite lateral directions (one of opposite second directions) from theneutral position, or, when a rightward directional operation ofperformed, the operation valve 55C changes a pressure of operation fluidoutput therefrom according to an operation amount of the rightwardoperation. When the traveling operation member 59 is swung leftward,i.e., in the other of the opposite lateral directions (that is, in theother of the opposite second directions), or when a leftward directionaloperation of performed), the operation valve 55D changes a pressure ofoperation fluid output therefrom according to an operation amount of theleftward directional operation.

The plurality of operation valves 55 and the traveling pumps 53L and 53Rare connected by the traveling fluid line 45. In other words, thetraveling pumps 53L and 53R are hydraulic equipment that are configuredto be operated by pilot fluid that is operation fluid output from theoperation valves 55 (that is, the operation valves 55A, 55B, 55C, and55D).

The traveling fluid line 45 has a first traveling fluid line 45 a, asecond traveling fluid line 45 b, a third traveling fluid line 45 c, afourth traveling fluid line 45 d, and a fifth traveling fluid line 45 e.The first traveling fluid line 45 a is a fluid line connected to apressure-receiving portion (referred to as a first pressure-receivingportion) 53 a of the left traveling pump 53L, and is a fluid linethrough which operation fluid having a pressure (a pilot pressure)applied to the first pressure-receiving portion 53 a flows when thetraveling operation member 59 is operated. The second traveling fluidline 45 b is a fluid line connected to a pressure-receiving portion(referred to as a second pressure-receiving portion) 53 b of the lefttraveling pump 53L, and is a fluid line through which operation fluidhaving a pressure (a pilot pressure) applied to the secondpressure-receiving portion 53 b flows when the traveling operationmember 59 is operated. The third traveling fluid line 45 c is a fluidline connected to a pressure-receiving portion (referred to as a thirdpressure-receiving portion) 53 a of the right traveling pump 53R, and isa fluid line through which operation fluid having a pressure (a pilotpressure) applied to the third pressure-receiving portion 53 a flowswhen the traveling operation member 59 is operated. The fourth travelingfluid line 45 d is a fluid line connected to a pressure-receivingportion (referred to as a fourth pressure-receiving portion) 53 b of theright traveling pump 53R, and is a fluid line through which operationfluid having a pressure (pilot pressure) applied to the fourthpressure-receiving portion 53 b flows when the traveling operationmember 59 is operated. The fifth traveling fluid line 45 e is a fluidline that connects the operation valves 55 to the first traveling fluidline 45 a, the second traveling fluid line 45 b, the third travelingfluid line 45 c, and the fourth traveling fluid line 45 d, respectively.

A plurality of high-pressure selector valves 47 a, 47 b, 47 c, and 47 dare located in the fifth traveling fluid line 45 e. The plurality ofhigh-pressure selector valves 47 a, 47 b, 47 c, and 47 d are connectedto the first traveling fluid line 45 a, the second traveling fluid line45 b, the third traveling fluid line 45 c, and the fourth travelingfluid line 45 d, respectively, and selectively supply operation fluidwith higher one of pressures (that is, the pilot pressure) therefrom.

When the traveling operation member 59 is swung forward (in a directionindicated by an arrowed line A1 in FIGS. 1 and 2), the operation valve55A is operated to output a pilot pressure. This pilot pressure isapplied to the pressure receiver portion 53 a of the left traveling pump53L via the first traveling fluid line 45 a and to the pressure receiverportion 53 a of the right traveling pump 53R via the third travelingfluid line 45 c. In this manner, the swash plate angles of the lefttraveling pump 53L and the right traveling pump 53R are changed, theleft traveling motor 36L and the right traveling motor 36R rotateforwardly (referred to as forward rotation), and the working machine 1travels straight forward.

When the traveling operation member 59 is swung backward (in a directionindicated by an arrowed line A2 in FIGS. 1 and 2), the operation valve55B is operated to output a pilot pressure. This pilot pressure isapplied to the pressure receiver portion 53 b of the left traveling pump53L via the second traveling fluid line 45 b and to the pressurereceiver portion 53 b of the right traveling pump 53R via the fourthtraveling fluid line 45 d. In this manner, the swash plate angles of theleft traveling pump 53L and the right traveling pump 53R are changed,the left traveling motor 36L and the right traveling motor 36R rotatereversely (referred to as backward rotation), and the working machine 1travels straight backward.

When the traveling control member 59 is swung to the right (in adirection indicated by an arrowed line A4 in FIGS. 1 and 2), the controlvalve 55C is operated to output a pilot pressure. This pilot pressure isapplied to the pressure receiver portion 53 a of the left traveling pump53L via the first traveling fluid line 45 a, and to the pressurereceiver portion 53 b of the right traveling pump 53R via the fourthtraveling fluid line 45 d. In this manner, the swash plate angles of theleft traveling pump 53L and the right traveling pump 53R are changed,and the left traveling motor 36L rotates forwardly and the righttraveling motor 36R rotates reversely, and the working machine 1 spinsto turn rightward (that is, spin turn).

When the traveling control member 59 is swung to the left (in adirection indicated by an arrowed line A3 in FIGS. 1 and 2), the controlvalve 55D is operated to output a pilot pressure. This pilot pressure isapplied to the pressure receiver portion 53 a of the right travelingpump 53R via the third traveling fluid line 45 c, and to the pressurereceiver portion 53 b of the left traveling pump 53L via the secondtraveling fluid line 45 b. In this manner, the swash plate angles of theleft traveling pump 53L and the right traveling pump 53R are changed,and the left traveling motor 36L rotates reversely and the righttraveling motor 36R rotates forwardly, and the working machine 1 spinsto turn leftward (that is, spin turn).

When the traveling operation member 59 is swung in an oblique direction(in a direction indicated by an arrowed line A5 in FIG. 2), rotationdirections and rotation speeds of the left traveling motor 36L and theright traveling motor 36R are determined by a differential pressurebetween the pilot pressures applied to the pressure receiving portion 53a and the pressure receiving portion 53 b, and the working machine 1pivots to turn rightward or leftward while it travels forward orbackward.

That is, when the traveling operation member 59 is swung obliquelyforward to the left, the working machine 1 turns to the left whiletraveling forward at a speed corresponding to the swing angle of thetraveling operation member 59. When the traveling operation member 59 isswung obliquely forward to the right, the working machine 1 turns to theright while traveling forward at a speed corresponding to the swingangle of the traveling operation member 59. When the traveling operationmember 59 is swung obliquely backward to the left, the working machine 1turns to the left while traveling backward at a speed corresponding tothe swing angle of the traveling operation member 59. In addition, whenthe traveling operation member 59 is swung obliquely backward to theright, the working machine 1 turns to the right while it travelsbackward at a speed corresponding to the swing angle of the travelingoperation member 59.

As shown in FIG. 1, the working machine 1 has a controller 60. Thecontroller 60 performs various controls of the working machine 1 and isconstituted of semiconductors such as a CPU, a MPU, electrical andelectronic circuits, or the like. A mode switch 66, a speed changerswitch 67, and a plurality of rotation detectors 68 are electricallyconnected to the controller 60.

The mode switch 66 is a switch configured to enable or disable automaticdeceleration. For example, the mode switch 66 is a switch capable ofbeing switched between on and off. The mode switch 66 when switched onenables the automatic deceleration, and the mode switch 66 when switchedoff disables the automatic deceleration.

The speed changer switch 67 is located in the vicinity of the driverseat 8 and can be operated by a driver (an operator). The speed changerswitch 67 is manually operable to shift each of rotation speed stages ofthe traveling motors 36L and 36R (that is, the left traveling motor 36Land right traveling motor 36R) to either the first speed or the secondspeed. For example, the speed changer switch 67 is a seesaw switchoperable to selectively perform either an accelerating operation forswitching rotation speeds of the traveling motors 36L and 36R from thefirst speed to the second speed, and a decelerating operation forshifting each of rotation speed stages of the traveling motors 36L and36R from the second speed to the first speed.

The plurality of rotation detectors 68 includes sensors and the like todetect the current rotation speeds (referred to as motor rotationspeeds) of the traveling motors 36L and 36R. The rotation detectors 68include a first rotation detector 68 a configured to detect a motorrotation speed of the left traveling motor 36L (referred to as a firstrotation speed) and a second rotation detector 68 b configured to detecta motor rotation speed of the right traveling motor 36R (referred to asa second rotation speed).

The controller 60 has an automatic decelerator 61. The automaticdecelerator 61 includes an electrical and electronic circuit or the likeinstalled in the controller 60, a computer program stored in thecontroller 60, or the like. The automatic decelerator 61 executes anautomatic deceleration control when automatic deceleration is enabled,and does not execute the automatic deceleration control when theautomatic deceleration is disabled.

In the automatic deceleration control, in a state where rotation speedsof the traveling motors 36L and 36R are each set at the second speed,the rotation speeds of the traveling motors 36L and 36R are eachautomatically reduced by shifting the rotation speed stage of each ofthe traveling motors 36L and 36R from the second speed to the firstspeed when a predetermined condition (referred to as an automaticdeceleration condition) is satisfied. In detail, in the automaticdeceleration control, when the automatic deceleration condition issatisfied at least in a state where the traveling motors 36L and 36R areeach set at the second speed, the controller 60 demagnetizes a solenoidof the second switching valve 72 to switch the second switching valve 72from the second position 72 b to the first position 72 a, and therotation speeds of the traveling motors 36L and 36R are reduced byshifting the rotation speed stage of each of the traveling motors 36Land 36R from the second speed to the first speed. That is, when theautomatic deceleration control is performed, the controller 60 reducesthe rotation speeds of both the left traveling motor 36L and the righttraveling motor 36R by shifting the rotation speed stage o ach of thetraveling motors 36L and 36R from the second speed to the first speed.

When a predetermined return condition is satisfied after the automaticdeceleration is performed, the automatic decelerator 61 magnetizes asolenoid of the second switching valve 72 to switch the second switchingvalve 72 from the first position 72 a to the second position 72 b, andincreases rotation speeds of the traveling motors 36L and 36R byshifting the rotation speed stage of each of the traveling motors 36Land 36R from the first speed to the second speed. That is, the rotationspeed stage of each of the traveling motors 36L and 36R returns to thesecond speed. In other words, the controller 60 increases the rotationspeeds of both the left traveling motor 36L and the right travelingmotor 36R by shifting the rotation speed stage of each of the travelingmotors 36L and 36R from the first speed to the second speed.

When the automatic deceleration is disabled, the controller 60 performsa manual switching control to switch the rotation speed stage of each ofthe traveling motors 36L and 36R to either the first speed or the secondspeed in response to operation of the speed changer switch 67. In themanual switching control, when the speed changer switch 67 is switchedto the first speed position, the solenoid of the second switching valve72 is demagnetized to set the rotation speeds of the traveling motors36L and 36R to the first speed. In the manual switching control, whenthe speed changer switch 67 is switched to the second speed, thesolenoid of the second switching valve 72 is magnetized to set therotation speeds of the traveling motors 36L and 36R to the second speed.Even in a state where the automatic deceleration is enabled, thecontroller 60 may switch the rotation speeds of the traveling motors 36Land 36R to either the first speed or the second speed in the manualswitching control when the speed changer switch 67 is operated.

The controller 60 is connected to an acceleration pedal 65 fordetermining a target revolving speed of the prime mover 32. Theacceleration pedal 65 is located in the vicinity of the driver seat 8.The acceleration pedal 65 is an acceleration lever supported swingably,an acceleration pedal supported swingably, an acceleration volumesupported rotatably, an acceleration slider supported slidably, or thelike. The acceleration pedal 65 is not limited to the examples describedabove. In addition, the controller 60 is connected to a third rotationdetector 69 configured to detect an actual revolving speed of the primemover 32. The third rotation detector 69 allows the controller 60 toacquire an actual revolving speed of the prime mover 32. Based on anoperation amount of the acceleration pedal 65, the controller 60determines a target revolving speed and controls the actual revolvingspeed until the actual rotation speed reaches the determined targetrevolving speed.

The controller 60 performs automatic deceleration based on pressures inthe circulation fluid lines 57 h and 57 i. A plurality of pressuredetectors 80 are connected to the circulation fluid lines 57 h and 57 i.The plurality of pressure detectors 80 include a first pressure detector80 a, a second pressure detector 80 b, a third pressure detector 80 c,and a fourth pressure detector 80 d. The first pressure detector 80 a isprovided on a portion of the first circulation fluid line 57 h extendedfrom one port of the left traveling pump and connected to a first portP11 of the left traveling motor 36L, and detects a first travelingpressure V1 that is a pressure of operation fluid flowing in the portionof the circulation fluid line 57 h connected to the first port P11. Thesecond pressure detector 80 b is provided on a portion of the firstcirculation fluid line 57 h extended from the other port of the lefttraveling pump 53L and connected to a second port P12 of the lefttraveling motor 36L, and detects a second traveling pressure V1 that isa pressure of operation fluid flowing in the portion of the firstcirculation fluid line 57 h connected to the second port P12. The thirdpressure detector 80 c is provided on a portion of the secondcirculation fluid lie 57 i extended from one port of the right travelingpump 53R and connected to a third port P13 of the right traveling motor36R, and detects a third traveling pressure V3 that is a pressure ofoperation fluid flowing in the portion of the second circulation fluidline 57 i connected to the third port P13. The fourth pressure detector80 d is provided on a portion of the second circulation fluid line 57 iextended from the other port of the right traveling pump 53R andconnected to a fourth port P14 of the right traveling motor 36R, anddetects a pressure of the operation fluid flowing in the portion of thesecond circulation fluid line 57 i connected to the fourth port P14. Theinstallation positions of the first pressure detector 80 a, the secondpressure detector 80 b, the third pressure detector 80 c, and the fourthpressure detector 80 d on the respective first and second circulationfluid lines 57 h and 57 i are not limited only if they are configured todetect respective pressures in the respective portions of the first andsecond circulation fluid lines 57 h and 57 i interposed between therespective ports of the left and right traveling pumps 53L and 53R andthe respective first, second, third and fourth ports P11, P12, P13 andP14 of the left and right traveling motors 36L and 36R.

The controller 60 (that is, the automatic decelerator 61) performsautomatic deceleration (a control processing to switch rotation speedsof the traveling motors 36L and 36R from the second speed to the firstspeed) based on the first traveling pressure V1 detected by the firstpressure detector 80 a, the second traveling pressure V2 detected by thesecond pressure detector 80 b, the third traveling pressure V3 detectedby the third pressure detector 80 c, and the fourth traveling pressureV4 detected by the fourth pressure detector 80 d.

When rotation speeds of the traveling motors 36L and 36R are set to thesecond speed and the machine body 2 (or the left traveling device 5L andthe right traveling device 5R) pivots to turn left, the controller 60refers to the third traveling pressure V3 and the fourth travelingpressure V4 corresponding to the right traveling motor 36R, and when thethird traveling pressure V3 or the fourth traveling pressure V4 is equalto or higher than a first left threshold ST1 _(L), the controller 60performs automatic deceleration. In addition, when the rotation speedsof the traveling motors 36L and 36R are set to the second speed and themachine body 2 pivots to turn right, the controller 60 refers to thefirst traveling pressure V1 and the second traveling pressure V2corresponding to the left traveling motor 36L, and when the firsttraveling pressure V1 or the second traveling pressure V2 is equal to orhigher than the first right threshold ST1 _(R), automatic decelerationis performed.

Timing of starting the pivot turn is when the traveling operation member59 is operated in the directions corresponding to the pivoting turn orwhen the machine body 2 shows behavior of the pivoting turn. A sensormay be provided to detect the operational directions of the travelingoperation member 59 shown in FIG. 2. Alternatively, a pressure detectormay be provided to detect a pilot pressure of the traveling fluid lines45 (that is, the first traveling fluid line 45 a, the second travelingfluid line 45 b, the third traveling fluid line 45 c, and the fourthtraveling fluid line 45 d), where pressures of operation fluid (that is,pilot pressures) are changed due to operation of the traveling operationmember 59; thus the controller 60 may detect the operational directionsof the traveling operation member 59 based on changing in pilotpressures detected by the pressure detection device. The method todetect the operational directions of the operation member 59 is notlimited to the above configuration, and may be performed in otherconfigurations and methods.

The controller 60 performs automatic deceleration based on the travelingpressures V1 to V4 as described above when the traveling operationmember 59 or the machine body 2 starts to pivot to turn left aftertraveling forward, starts to pivot to turn right after travelingforward, starts to pivot to turn left after traveling backward, andstarts to pivot to turn right after traveling backward.

In the above-described embodiment, in a case where operation of thetraveling operation member 59 or behavior of the machine body 2 showstiming of starting the left pivot turn, it is determined whether toperform automatic deceleration when the third traveling pressure V3 orthe fourth traveling pressure V4 is equal to or higher than the firstleft threshold ST1 _(L), and in a case where operation of the travelingoperation member 59 or behavior of the machine body 2 shows timing ofstarting the right pivot turn, it is determined whether to performautomatic deceleration when the first traveling pressure V1 or thesecond traveling pressure V2 is equal to or higher than the first rightthreshold ST1 _(R). In addition to this configuration, it is alsopossible to determine whether to perform automatic deceleration based oneffective differential pressures between the traveling pressures V1 toV4 as follows.

For example, in a case where rotation speeds of the traveling motors 36Land 36R are set to the second speed and the machine body 2 pivots toturn left, the controller 60 calculates the effective third differentialpressure ΔV3 (that is, a value obtained by subtracting the fourthtraveling pressure V4 from the third traveling pressure V3)corresponding to the right traveling motor 36R and the effective fourthdifferential pressure ΔV4 (that is, a value obtained by subtracting thethird traveling pressure V3 from the fourth traveling pressure V4)corresponding to the right traveling motor 36R. When the thirddifferential pressure ΔV3 or the fourth differential pressure ΔV4 isequal to or higher than the second left threshold ST2 _(L), thecontroller 60 performs automatic deceleration.

In the case where rotation speeds of the traveling motors 36L and 36Rare set to the second speed and the machine body 2 pivots to turn right,the controller 60 calculates the effective first differential pressureΔV1 (that is, a value obtained by subtracting the second travelingpressure V2 from the first traveling pressure V1) corresponding to theleft traveling motor 36L and the effective second differential pressureΔV2 (that is, a value obtained by subtracting the first travelingpressure V1 from the second traveling pressure V2) corresponding to theleft traveling motor 36L. When the first differential pressure ΔV1 orthe second differential pressure ΔV2 is equal to or higher than thesecond right threshold ST2 _(R), the controller 60 performs automaticdeceleration.

The controller 60 determines the left thresholds (that is, the firstleft threshold ST1 _(L) and the second left threshold ST2 _(L)) to beused in left pivot turn and the right thresholds (that is, the firstright thresholds ST1 _(R) and the second right thresholds ST2 _(R)) tobe used in right pivot turn, based on rotation speeds of the travelingmotors 36L and 36R. That is, the controller 60 determines the leftthreshold and the right threshold as deceleration thresholds for judgingdeceleration of automatic deceleration based on rotation speeds of thetraveling motors 36L and 36R. For convenience of explanation, therotation speed of the left traveling motor 36L is hereinafter referredto as a “first rotation speed LM_(RPM)”, and the rotation speed of theright traveling motor 36R as a “second rotation speed RM_(RPM).”

FIG. 3 shows the relationship between the left thresholds (that is, thefirst left threshold ST1 _(L) and the second left threshold ST2 _(L))and the second rotation speed RM_(RPM). FIG. 3 shows two left thresholdsfor convenience of explanation, the first left threshold ST1 _(L) andthe second left threshold ST2 _(L), for the second rotation speedRM_(RPM); however, the controller 60 needs determine any one of thefirst left threshold ST1 _(L) and the second left threshold ST2 _(L).

As shown in FIG. 3, the controller 60 determines the left thresholds(that is, the first left threshold ST1 _(L) and the second leftthreshold ST2 _(L)) to be lower as the second rotation speed RM_(RPM)decreases, and determines the left thresholds to be higher as the secondrotation speed RM_(RPM) increases. In addition, the controller 60 maydetermine the left thresholds (that is, the first left threshold ST1_(L) and the second left threshold ST2 _(L)) by applying the secondrotation speed RM_(RPM) detected by the second rotation detector 68 b tolines L1 and L2 representing relationships between the second rotationspeed RM_(RPM) and the left thresholds (that is, the first leftthreshold ST1 _(L) and the second left threshold ST2 _(L)) as shown inFIG. 3. Alternatively, control data such as equations (that is, linearfunction equations representing the lines L1 and L2 in FIG. 3) or atable, which show the relationships between the second rotation speedRM_(RPM) and the left thresholds ST1 _(L) and ST2 _(L), may be stored inthe storage 63 in advance, and the controller 60 may determine the leftthresholds (that is, the first left threshold ST1 _(L) and the secondleft threshold ST2 _(L)) by extracting the first left threshold ST1 _(L)and second left threshold ST2 _(L) corresponding to the second rotationspeed RM_(RPM) from the control data.

FIG. 4 shows relationships between the right thresholds (that is, thefirst right threshold STIR and the second right threshold ST2 _(R)) andthe first rotation speed LM_(RPM). For convenience of explanation, FIG.3 shows two right thresholds, the first right threshold ST1 _(R) and thesecond right threshold ST2 _(R), for the first rotation speed LM_(RPM);however, the controller 60 needs determine any one of the first rightthreshold ST1 _(R) and the second right threshold ST2 _(R).

As shown in FIG. 4, the controller 60 determines the right thresholds(that is, the first right threshold ST1 _(R) and the second rightthreshold ST2 _(R)) to be lower as the first rotation speed LM_(RPM)decreases, and determines the right thresholds to be higher as the firstrotation speed LM_(RPM) increases. The controller 60 may determine theright thresholds (that is, the first right threshold STIR and the secondright threshold ST2 _(R)) by applying the first rotation speed LM_(RPM)detected by the first rotation detector 68 a to lines L3 and L4 showingthe relationships between the first rotation speed LM_(RPM) and theright thresholds (that is, the first right threshold ST1 _(R) and thesecond right threshold ST2 _(R)) as shown in FIG. 4. Alternatively,control data such as an equations (that is, linear function equationsrepresenting the lines L3 and L4 in FIG. 4) or a table showing therelationships between the first rotation speed LM_(RPM) and the firstright threshold ST1 _(R) and the second right threshold ST2 _(R) may bestored in the storage 63 in advance, and the controller 60 may determinethe right thresholds (that is, the first right threshold ST1 _(R) andthe second right threshold ST2 _(R)) by extracting the first rightthreshold STIR and the second right threshold ST2 _(R) corresponding tothe first rotation speed LM_(RPM) detected by the first rotationdetector 68 a from the control data.

The controller 60 performs automatic deceleration in left pivot turnbased on the left thresholds (that is, the first left threshold ST1 _(L)and the second left threshold ST2 _(L)) determined according to thesecond rotation speed RM_(RPM) of the right traveling motor 36R on theopposite side of the left traveling motor 36L. In addition, thecontroller 60 performs automatic deceleration in right pivot turn basedon the right thresholds (that is, the first right threshold ST1 _(R) andthe second left threshold ST2 _(L)) determined according to the firstrotation speed LM_(RPM) of the left traveling motor 36L on the oppositeside of the right traveling motor 36R.

In detail, the controller 60 refers to the second rotation speedRM_(RPM) to determine the first left threshold ST1 _(L) in left pivotturn. After determination of the first left threshold ST1 _(L), thecontroller 60 performs automatic deceleration when the third travelingpressure V3 or the fourth traveling pressure V4 is equal to or higherthan the first left threshold ST1 _(L). Alternatively, the controller 60refers to the second rotation speed RM_(RPM) to determine the secondleft threshold ST2 _(L) in left pivot turn. After determination of thesecond left threshold ST2 _(L), the controller 60 performs automaticdeceleration when the third differential pressure ΔV3 or the fourthdifferential pressure ΔV4 is equal to or higher than the second leftthreshold ST2 _(L).

The controller 60 refers to the first rotation speed LM_(RPM) todetermine the first right threshold ST1 _(R) in right pivot turn. Afterdetermination of the first right threshold ST1 _(R), the controller 60performs automatic deceleration when the first traveling pressure V1 orthe second traveling pressure V2 is equal to or higher than the firstright threshold ST1 _(R). Alternatively, the controller 60 refers to thefirst rotation speed LM_(RPM) to determine the second right thresholdST2 _(R) in right pivot turn. After determination of the second rightthreshold ST2 _(R), the controller 60 performs automatic decelerationwhen the first differential pressure ΔV1 or the second differentialpressure ΔV2 is equal to or higher than the second right threshold ST2_(R).

The controller 60 may change the left thresholds (that is, the firstleft threshold ST1 _(L) and the second left threshold ST2 _(L)) and theright thresholds (that is, the first right threshold ST1 _(R) and thesecond right threshold ST2 _(R)) according to a revolving speed of theprime mover 32.

In the above-described embodiment, as shown in FIGS. 3 and 4, the leftand right thresholds (that is, the first left threshold ST1 _(L), secondleft threshold ST2 _(L), first right threshold STIR, and second rightthreshold ST2 _(R)) are determined based on the rotation speeds LM_(RPM)and RM_(RPM); however, automatic deceleration does not have to beperformed when the rotation speeds LM_(RPM) and RM_(RPM) are apredetermined threshold M30 or above, that is, when rotation speeds ofthe traveling motors 36L and 36R are in a speed range from the maximumspeed to the threshold M30. For convenience of explanation, the leftthresholds (that is, the first left threshold ST1 _(L) and second leftthreshold ST2 _(L)) and right thresholds (that is, the first rightthreshold ST1 _(R) and second right threshold ST2 _(R)) at the firstspeed LM_(RPM) and second speed RM_(RPM) are determined at the thresholdM30 or below (that is, the lines L1 and L2 end at the threshold M30);however, there is no problem if the calculation of the left and rightthresholds is performed above the threshold M30.

When the machine body 2 spins to turn, the controller 60 determinesspin-turn thresholds (that is, the first spin-turn threshold ST1 _(P)and the second spin-turn threshold ST2 _(P)), which are decelerationthresholds, to be lower than the left and right thresholds for thepivoting to turn. In addition, the controller 60 determines thespin-turn threshold according to higher (that is, faster) one of thefirst rotation speed LM_(RPM) of the left traveling motor 36L and thesecond rotation speed RM_(RPM) of the right traveling motor 36R.

Then, in a case where rotation speeds of the traveling motors 36L and36R are determined to the second speed and the machine body 2 (or theleft traveling device 5L and the right traveling device 5R) spins toturn right or left, the controller 60 performs automatic decelerationwhen any one of the first traveling pressure V1, the second travelingpressure V2, the third traveling pressure V3, and the fourth travelingpressure V4 is equal to or higher than the first spin-turn threshold ST1_(P).

Alternatively, in a case where rotation speeds of the traveling motors36L and 36R are determined to the second speed and the machine body 2spins to turn right or left, the controller 60 performs automaticdeceleration when any one of the first differential pressure ΔV1, thesecond differential pressure ΔV2, the third differential pressure ΔV3,and the fourth differential pressure ΔV4 is equal to or higher than thesecond spin-turn threshold ST2 _(P).

In a case where rotation speeds of the traveling motors 36L and 36R aredetermined to the second speed and the machine body 2 travels straightforward (that is, forward traveling), the controller 60 performsautomatic deceleration when either the first traveling pressure V1 orthe third traveling pressure V3 is equal to or higher than the firststraight-traveling threshold SF1 _(S).

Alternatively, in a case where rotation speeds of the traveling motors36L and 36R are determined to the second speed and the machine body 2travels straight forward, the controller 60 performs automaticdeceleration when either the first differential pressure ΔV1 or thethird differential pressure ΔV3 is equal to or higher than the secondstraight-traveling threshold SF2 _(S).

Timing of straight traveling of the machine body 2 is when the travelingoperation member 59 is operated in the directions corresponding toforward straight traveling or backward straight traveling or when themachine body 2 shows behavior of the forward straight traveling or thebackward straight traveling. An operation of forward or backwardstraight traveling by the traveling operation member 59 can be detectedby a sensor, a pressure detector, or the like, in the same manner as theabove-described pivoting to turn. In addition, when an operationaldirection of the traveling operation member 59 changes from the pivotturn direction to the straight-traveling direction, the controller 60judges whether to perform automatic deceleration based on thestraight-traveling threshold described below. The operation of thetraveling operation member 59 for straight traveling is to tilt thetraveling operation member 59 to the forward direction and the backwarddirection, as shown in FIG. 2. And, even when the operational directionof the traveling operation member 59 is oblique, the operation isincluded in the operation for straight traveling when being in apredetermined range allowable for the operation for straight traveling.

The controller 60 determines the straight-traveling thresholds (that is,the first straight-traveling threshold SF1 _(S) and the secondstraight-traveling threshold SF2 _(S)) based on the rotation differenceΔMP between the first rotation speed LM_(RPM) detected by the firstrotation detector 68 a and the second rotation speed RM_(RPM) detectedby the second rotation detector. The rotation difference ΔMP may be avalue obtained by subtracting the second rotation speed RM_(RPM) fromthe first rotation speed LM_(RPM), or a value obtained by subtractingthe first rotation speed LM_(RPM) from the second rotation speedRM_(RPM). If the rotation difference ΔMP is a negative value, therotation difference ΔMP shall be an absolute value.

FIG. 5 shows a relationship between the straight-traveling thresholds(that is, the first straight-traveling threshold SF1 _(S) and the secondstraight-traveling threshold SF2 _(S)) and the rotation difference ΔMP.For convenience of explanation, FIG. 5 shows two straight-travelingthresholds, the first straight-traveling threshold SF1 _(S) and thesecond straight-traveling threshold SF2 _(S), for the rotationdifference ΔMP; however, the controller 60 only needs to determineeither the first straight-traveling threshold SF1 _(S) or the secondstraight-traveling threshold SF2 _(S).

As shown in FIG. 5, the controller 60 determines the straight-travelingthresholds (that is, the first straight-traveling threshold SF1 _(S) andthe second straight-traveling threshold SF2 _(S)) to be higher as therotation difference ΔMP increases, and determines the straight-travelingthreshold to be lower as the rotation difference ΔMP decreases. As shownin FIG. 5, the controller 60 may determine the first straight-travelingthreshold SF1 _(S) and the second straight-traveling threshold SF2 _(S)by applying the calculated rotation difference ΔMP to lines L5 and L6that show the relationships between the straight-traveling thresholdsSF1 _(S) s and SF2 _(S) and the rotation difference ΔMP. Alternatively,control data such as equations (that is, linear function equationsrepresenting the lines L5 and L6 in FIG. 5) or a table showing therelationships between the rotation difference ΔMP and thestraight-traveling thresholds SF1 _(S) and SF2 _(S) may be stored in thestorage 63 in advance, and the controller 60 may extract the firststraight-traveling threshold SF1 _(S) and the second straight-travelingthreshold SF2 _(S) corresponding to the calculated rotation differenceΔMP from the control data.

That is, the controller 60 performs automatic deceleration based on thestraight-traveling thresholds (that is, the first straight-travelingthreshold SF1 _(S) and the second straight-traveling threshold SF2 _(S))determined according to the rotation difference ΔMP between the firstrotation speed LM_(RPM) and the second rotation speed RM_(RPM) intraveling straight forward, that is, in forward traveling.

In detail, the controller 60 refers to the first rotation speed LM_(RPM)and the second rotation speed RM_(RPM) in forward traveling to calculatethe rotation difference ΔMP, and determines the first straight-travelingthreshold SF1 _(S) according to the calculated rotation difference ΔMP.After determination of the first straight traveling threshold SF1 _(S),the controller 60 performs automatic deceleration when the firsttraveling pressure V1 or the third traveling pressure V3 is equal to orhigher than the first straight traveling threshold SF1 _(S).Alternatively, the controller 60 calculates the rotation difference ΔMPin forward traveling, and determines the second straight travelingthreshold SF2 _(S) according to the calculated rotation difference ΔMP.After determination of the second straight traveling threshold SF2 _(S),the controller 60 performs automatic deceleration when the firstdifferential pressure ΔV1 or the third differential pressure ΔV3 isequal to or higher than the second straight traveling threshold SF2_(S).

In the embodiment described above, the first straight-travelingthreshold SF1 _(S) and the second straight-traveling threshold SF2 _(S)are acquired based on the rotation difference Δ MP; alternatively, thefirst straight-traveling threshold SF1 _(S) and the secondstraight-traveling threshold SF2 _(S) may be acquired based on arotation-ratio difference ΔDP. The rotation-ratio difference ΔDP is adifference between a first ratio acquired by dividing the secondrotation speed RM_(RPM) by the first rotation speed LM_(RPM) and asecond ratio acquired by dividing the first rotation speed LM_(RPM) bythe second rotation speed RM_(RPM). If the rotation-ratio difference ΔDPis a negative value, the absolute value shall be applied.

The controller 60 acquires the rotation-ratio difference ΔDP using thefirst rotation speed LM_(RPM) and the second rotation speed RM_(RPM),and determines the straight-traveling thresholds (that is, the firststraight-traveling threshold SF1 _(S) and the second straight-travelingthreshold SF2 _(S)) based on the rotation-ratio difference ΔDP.

FIG. 6A shows relationships between the straight-traveling thresholds(that is, the first straight-traveling threshold SF1 _(S) and the secondstraight-traveling threshold SF2 _(S)) and the rotation-ratio differenceΔDP. For convenience of explanation, FIG. 6 shows two straight-travelingthresholds, the first straight-traveling threshold SF1 _(S) and thesecond straight-traveling threshold SF2 _(S), for the rotation-ratiodifference ΔDP, but the controller 60 only needs to determine any one ofthe first straight-traveling threshold SF1 _(S) and the secondstraight-traveling threshold SF2 _(S).

As shown in FIG. 6A, the controller 60 determines the straight-travelingthresholds (that is, the first straight-traveling threshold SF1 _(S) andthe second straight-traveling threshold SF2 _(S)) to be higher as therotation-ratio difference ΔDP increases, and determines thestraight-traveling threshold to be lower as the rotation-ratiodifference ΔDP decreases. As shown in FIG. 6A, the controller 60 maydetermine the first straight-traveling threshold SF1 _(S) and the secondstraight-traveling threshold SF2 _(S) by applying the calculatedrotation-ratio difference ΔDP to lines L7 and L8 that show therelationships between the straight-traveling thresholds SF1 _(S) and SF2_(S) and the rotation-ratio difference ΔDP. Alternatively, control datasuch as equations (that is, linear function equations representing thelines L7 and L8 in FIG. 6A) or a table showing the relationships betweenthe rotation-ratio difference ΔDP and the straight-traveling thresholdsSF1 _(S) and SF2 _(S) may be stored in the storage 63 in advance, andthe controller 60 may determine the first straight-traveling thresholdSF1 _(S) and the second straight-traveling threshold SF2 _(S) byextracting the first straight-traveling threshold SF1 _(S) and thesecond straight-traveling threshold SF2 _(S) corresponding to thecalculated rotation-ratio difference ΔDP from the control data.

That is, in forward traveling, the controller 60 performs automaticdeceleration based on the straight-traveling thresholds (that is, thefirst straight-traveling threshold SF1 _(S) and the secondstraight-traveling threshold SF2 _(S)) determined based on therotation-ratio difference ΔDP between the first rotation speed LM_(RPM)and the second rotation speed RM_(RPM).

In detail, the controller 60 refers to the first rotation speed LM_(RPM)and the second rotation speed RM_(RPM) in forward traveling to calculatethe rotation-ratio difference ΔDP, and determines the firststraight-traveling threshold SF1 _(S) based on the calculatedrotation-ratio difference ΔDP. After determination of the first straighttraveling threshold SF1 _(S), the controller 60 performs automaticdeceleration when the first traveling pressure V1 or the third travelingpressure V3 is equal to or higher than the first straight travelingthreshold SF1 _(S). Alternatively, the controller 60 calculates therotation-ratio difference ΔDP in forward traveling, and determines thesecond straight traveling threshold SF2 _(S) based on the calculatedrotation-ratio difference ΔDP. After determination of the secondstraight-traveling threshold SF2 _(S), the controller 60 performsautomatic deceleration when the first differential pressure ΔV1 or thethird differential pressure ΔV3 is equal to or higher than the secondstraight-traveling threshold SF2 _(S).

In the above-described embodiment, the straight-traveling thresholds(that is, the first straight-traveling threshold SF1 _(S) and the secondstraight-traveling threshold SF2 _(S)) are determined based on therotation-ratio difference ΔDP, but the straight-traveling thresholds(that is, the first straight-traveling threshold SF1 _(S) and the secondstraight-traveling threshold SF2 _(S)) may be determined based on aratio (that is, a rotation ratio) ΔDQ between the first rotation speedLM_(RPM) and the second rotation speed RM_(RPM).

As shown in FIG. 6B, the controller 60 determines the straight-travelingthresholds (that is, the first straight-traveling threshold SF1 _(S) andthe second straight-traveling threshold SF2 _(S)) to be higher as therotation ratio ΔDQ decreases, and determines the straight-travelingthreshold to be lower as the rotation ratio ΔDQ increases. As shown inFIG. 6B, the controller 60 may determine the first straight-travelingthreshold SF1 _(S) and the second straight-traveling threshold SF2 _(S)by applying the calculated rotation ratio ΔDQ to lines L9 and L10 thatshow the relationships between the straight-traveling thresholds SF1_(S) and SF2 _(S) and the rotation ratio ΔDQ. Alternatively, controldata such as equations (that is, linear function equations representingthe lines L9 and L10 in FIG. 6B) or a table showing the relationshipsbetween the rotation ratio ΔDQ and the straight-traveling thresholds SF1_(S) and SF2 _(S) may be stored in the storage 63 in advance, and thecontroller 60 may determine the first straight-traveling threshold SF1_(S) and the second straight-traveling threshold SF2 _(S) by extractingthe first straight-traveling threshold SF1 _(S) and the secondstraight-traveling threshold SF2 _(S) corresponding to the calculatedrotation ratio ΔDQ from the control data.

That is, the controller 60 performs automatic deceleration in forwardtraveling based on the straight-traveling thresholds (that is, the firststraight-traveling threshold SF1 _(S) the second straight-travelingthreshold SF2 _(S)) determined by the rotation ratio ΔDQ between thefirst rotation speed LM_(RPM) and the second rotation speed RM_(RPM).

In detail, the controller 60 refers to the first rotation speed LM_(RPM)and the second rotation speed RM_(RPM) in forward traveling to calculatethe rotation ratio ΔDQ, and determines the first straight-travelingthreshold SF1 _(S) based on the calculated rotation ratio ΔDQ. Afterdetermination of the first straight traveling threshold SF1 _(S), thecontroller 60 performs automatic deceleration when the first travelingpressure V1 or the third traveling pressure V3 is equal to or higherthan the first straight traveling threshold SF1 _(S). Alternatively, thecontroller 60 calculates the rotation ratio ΔDQ in forward traveling,and determines the second straight traveling threshold SF2 _(S) based onthe calculated rotation ratio ΔDQ. After determination of the secondstraight-traveling threshold SF2 _(S), the controller 60 performsautomatic deceleration when the first differential pressure ΔV1 or thethird differential pressure ΔV3 is equal to or higher than the secondstraight-traveling threshold SF2 _(S).

In the above-described embodiment, the first straight-travelingthreshold SF1 _(S) and the second straight-traveling threshold SF2 _(S)are determined based on the rotation difference ΔMP or therotation-ratio difference ΔDP, but alternatively, the firststraight-traveling threshold SF1 _(S) and the second straight-travelingthreshold SF2 _(S) may be determined based on the first rotation speedLM_(RPM) and the second rotation speed RM_(RPM).

As shown in FIG. 7, the controller 60 determines the straight-travelingthresholds (that is, the first straight-traveling threshold SF1 _(S) andthe second straight-traveling threshold SF2 _(S)) to be lower as thefirst speed LM_(RPM) and the second speed RM_(RPM) decrease, anddetermines the straight-traveling thresholds to be higher as the firstspeed LM_(RPM) and the second speed RM_(RPM) increase. As shown in FIG.7, the controller 60 may determine first straight-traveling thresholdSF1 _(S) and the second straight-traveling threshold SF2 _(S) byapplying the first rotation speed LM_(RPM) detected by the firstrotation detector 68 a and the second rotation speed RM_(RPM) detectedby the second rotation detector 68 b to lines L11 and L12 showing therelationships between the straight-traveling thresholds SF1 _(S) and SF2_(S) and the rotation speeds LM_(RPM) and RM_(RPM). Alternatively,control data such as equations (that is, linear function equationsrepresenting the lines L11 and L12 in FIG. 7) or a table showing therelationships between the rotation speeds LM_(RPM) and RM_(RPM) and thestraight-traveling thresholds SF1 _(S) s and SF2 _(S) may be stored inthe storage 63 in advance, and the controller 60 may determine the firststraight-traveling threshold SF1 _(S) s and the secondstraight-traveling threshold SF2 _(S) by extracting the firststraight-traveling threshold SF1 _(S) and the second straight-travelingthreshold SF2 _(S) corresponding to the first rotation speed LM_(RPM)and the second rotation speed RM_(RPM) from the control data.

That is, the controller 60 performs automatic deceleration based on thestraight-traveling thresholds (that is, the first straight-travelingthreshold SF1 _(S) and the second straight-traveling threshold SF2 _(S))determined by the first rotation speed LM_(RPM) and the second rotationspeed RM_(RPM) in forward traveling.

In detail, the controller 60 refers to the first rotation speed LM_(RPM)and the second rotation speed RM_(RPM) in forward traveling, anddetermines the first straight-traveling threshold SF1 _(S) based on thefirst rotation speed LM_(RPM) and the second rotation speed RM_(RPM).After determination of the first straight traveling threshold SF1 _(S),the controller 60 performs automatic deceleration when both the firsttraveling pressure V1 and the third traveling pressure V3 arecontinuously equal to or higher than the first straight travelingthreshold SF1 _(S). In detail, when a length of time (that is, elapsedtime) during which both the first traveling pressure V1 and the thirdtraveling pressure V3 are equal to or higher than the first straighttraveling threshold SF1 _(S) is equal to or longer than a first judgmenttime, the controller 60 performs automatic deceleration. The controller60 determines the first judgment time to be shorter as the firstrotation speed LM_(RPM) or the second rotation speed RM_(RPM) increase,and determines the first judgment time to be longer as the firstrotation speed LM_(RPM) or the second rotation speed RM_(RPM) decrease.

Alternatively, in forward traveling, the controller 60 refers to thefirst rotation speed LM_(RPM) and the second rotation speed RM_(RPM),and determines the second straight-traveling threshold SF2 _(S) based onthe first rotation speeds LM_(RPM) and the second rotation speedRM_(RPM). After determination of the second straight-traveling thresholdSF2 _(S), the controller 60 performs automatic deceleration when boththe first differential pressure ΔV1 and the third differential pressureΔV3 are continuously equal to or higher than the secondstraight-traveling thresholds SF2 _(S). In detail, when a length of time(that is, elapsed time) during which both the first differentialpressure ΔV1 and the third differential pressure ΔV3 are equal to orhigher than the second straight-traveling thresholds SF2 _(S) is equalto or longer than a second judgment time, the controller 60 performsautomatic deceleration. The controller 60 determines the second judgmenttime to be shorter as the first speed LM_(RPM) or the second speedRM_(RPM) increase, and determines the second judgment time to be longeras the first speed LM_(RPM) or the second speed RM_(RPM) decrease.

In the above-described embodiment, the controller 60 does not performautomatic deceleration when the traveling operation member 59 isoperated in a direction for forward traveling of the machine body 2 andthe left traveling motor 36L and the right traveling motor 36R arerotating in a direction corresponding to backward traveling of themachine body 2 backward, that is, in reversely rotating.

The controller 60 does not perform automatic deceleration when the firstrotation speed LM_(RPM) of the left traveling motor 36L is equal to orhigher than a predetermined rotation speed, or when the second rotationspeed RM_(RPM) of the right traveling motor 36R is equal to or higherthan a predetermined rotation speed. For example, the controller 60 doesnot perform automatic deceleration when the first rotation speedLM_(RPM) of the left traveling motor 36L is equal to or higher than afirst maximum rotation speed of the left traveling motor 36L. Thecontroller 60 does not perform automatic deceleration when the secondrotation speed RM_(RPM) of the right traveling motor 36R is equal to orhigher than a second maximum rotation speed of the right traveling motor36R. According to this configuration, workability can be improvedwithout performing automatic deceleration when the first rotation speedLM_(RPM) and the second rotation speed RM_(RPM) are at high speeds.

In the above-described embodiment, the hydraulic traveling operationdevice 54 configured to change a pilot pressure applied to the travelingpumps (that is, the first traveling pump 53L and the second travelingpump 53R) using the operation valves 55, but alternatively, anelectrically-operated traveling operation device 54 may be used as shownin FIGS. 8A and 8B, for example. In this case, the traveling operationmember 59 may be constituted of an electrically-actuated operationmember such as a joystick.

The traveling operation device 54 shown in FIG. 8A has the operationvalves 55 a, 55 b, 55 c, and 55 d, which are constituted of solenoidproportional valves. The controller 60 is connected to an operationdetection sensor 161 to detect an operation extent and operationaldirections of the operation member 59 that is swung in the lateraldirection (that is, the machine width direction) or the fore-and-aftdirection. The controller 60 controls the operation valves 55 a, 55 b,55 c, and 55 d based on the operation extent and operational directionsof the operation member 59 detected by the operation detection sensor161.

When the operating member 59 is operated forward (in a direction A1 inFIG. 2), the controller 60 outputs a control signal to the operationvalve 55 a and the operation valve 55 c to turn the swash plates of thefirst traveling pump 53L and the second traveling pump 53R in respectivedirections for normal rotation of the left traveling motor 36L and theright traveling motor 36R (that is, forward traveling of the left andright traveling devices 5), thereby rotating the left and righttraveling motors 36L and 36R forward (normally).

When the operating member 59 is operated backward (in a direction A2 inFIG. 2), the controller 60 outputs a control signal to the operationvalve 55 b and the operation valve 55 d to turn the swash plates of thefirst traveling pump 53L and the second traveling pump 53R in respectivedirections for reverse rotation of the left traveling motor 36L and 36R(that is, backward traveling of the left and right traveling devices 5),thereby rotating the left and right traveling motors 36L and 36Rbackward (reversely).

When the operating member 59 is operated rightward (in a direction A4 inFIG. 2), the controller 60 outputs a control signal to the operationvalve 55 a and the operation valve 55 d to turn the swash plate of thefirst traveling pump 53L in the direction for normal rotation of theleft traveling motor 36L and to turn the swash plate of the secondtraveling pump 53R in the direction for reverse rotation of the righttraveling motor 36R, thereby rotating the first traveling pump 53Lnormally, and rotating the second traveling pump 53R reversely.

Further, when the operating member 59 is operated leftward (in adirection A3 in FIG. 2), the controller 60 outputs a control signal tothe operation valve 55 b and the operation valve 55 c to turn the swashplate of the first traveling pump 53L in the direction for reverserotation of the left traveling motor 36L and to turn the swash plate ofthe second traveling pump 53R in the direction for normal rotation ofthe right traveling motor 36R, thereby rotating the left traveling motor36L reversely, and rotating the right traveling motor 36R normally.

The traveling operation device 54 shown in FIG. 8B has operation valves155L and 155R and hydraulic regulators 156L and 156R. Each of thehydraulic regulators 156L and 156R has a supply chamber 157 to whichoperation fluid can be supplied and a piston rod 158 located in thesupply chamber 157. The piston rod 158 of the hydraulic pressureregulator 156L is connected to the swash plate of the first travelingpump 53L. The piston rod 158 of the hydraulic pressure regulator 156R isconnected to the swash plate of the second traveling pump 53R. Angles ofthe swash plates of traveling pumps 53L and 53R are changed due to theoperations (in straight-line movements) of the piston rods 158 of thehydraulic regulators 156L and 156R.

The operation valve 155L is a solenoid proportional valve to operate thehydraulic regulator 156L and is switchable between a first position 159a, a second position 159 b, and a neutral position 159 c. The positionsof the operation valve 155L are changed through movement of the spool ofthe valve 155L based on the control signal output from the controller60. A first port of the operation valve 155L is connected to the supplychamber 157 of the hydraulic regulator 156L by the first traveling fluidline 145 a. A second port of the operation valve 155L is connected tothe supply chamber 157 of the hydraulic regulator 156L by the secondtraveling fluid line 145 b.

The operation valve 155R is a solenoid proportional valve to operate thehydraulic regulator 156R and is switchable between a first position 159a, a second position 159 b, and a neutral position 159 c. The positionsof the operation valve 155R are changed through movement of the spool ofthe valve 155R based on the control signal output from the controller60. A first port of the operation valve 155R is connected to the supplychamber 157 of the hydraulic regulator 156R by the third traveling fluidline 145 c. A second port of the operation valve 155R is connected tothe supply chamber 157 of the hydraulic regulator 156R by the fourthtraveling fluid line 145 d.

The controller 60 outputs a control signal to the operation valve 155Land the operation valve 155R to switch the operation valve 155L and theoperation valve 155R to the first position 159 a. In this manner, theswash plates of the first traveling pump 53L and the second operatingpump 53R turn in the respective directions for normal rotation of theleft and right traveling motors 36L and 36R, and thereby rotating thefirst traveling pump 53L and the second traveling pump 53R normally.

The controller 60 outputs a control signal to the operation valve 155Land the operation valve 155R to switch the operation valve 155L and theoperation valve 155R to the second position 159 b. In this manner, theswash plates of the first traveling pump 53L and the second operatingpump 53R turn in the respective directions for reverse rotation of theleft and right traveling motors 36L and 36R, and thereby rotating thefirst traveling pump 53L and the second traveling pump 53R reversely.

In addition, the controller 60 outputs a control signal to the operationvalve 155L and the operation valve 155R to switch the operation valve155L to the first position 159 a and to switch the operation valve 155Rto the second position 159 b. In this manner, the swash plate of thefirst traveling pump 53L turns in the direction for normal rotation ofthe left and right traveling motors 36L and 36R, thereby rotating thefirst traveling pump 53L normally, and the swash plate of the secondoperating pump 53R turns in the direction for reverse rotation of theright traveling motor 36R, thereby rotating the second traveling pump53R reversely.

Further, the controller 60 outputs a control signal to the operationvalve 155L and the operation valve 155R to switch the operation valve155L to the second position 159 b and to switch the operation valve 155Rto the first position 159 a. In this manner, the swash plate of thefirst traveling pump 53L turns in the direction for reverse rotation ofthe left traveling motor 36L, thereby rotating the first traveling pump53L reversely, and the swash plate of the second operating pump 53Rturns in the direction for forward rotation of the right traveling motor36R, thereby rotating the second traveling pump 53R normally.

Electric actuators such as the solenoid proportional valves 155 a to 155d, 155L, and 155R described above may be used to change the angles ofthe swash plates of the traveling motors 36L and 36R.

According to the above embodiment, the working machine 1 has thestructures and provides effects as follows.

The working machine 1 incudes the machine body 2, the left travelingdevice 5L located left on the machine body 2, the right traveling device5R located right on the machine body 2, the left traveling motor 36L tooutput a power transmitted to the left traveling device 5L, the righttraveling motor 36R to output a power transmitted to the right travelingdevice 5R, the first rotation detector 68 a to detect the first rotationspeed LM_(RPM) of the left traveling motor 36L, the second rotationdetector 68 b to detect the second rotation speed RM_(RPM) of the righttraveling motor 36R, the left traveling pump 53L to supply operationfluid to the left traveling motor 36L, the right traveling pump 53R tosupply operation fluid to the right traveling motor 36L, the travelingoperation device 54 to operate at least one of the left traveling pump53L and the right traveling pump 53R, and the controller 60 configuredor programmed to perform automatic deceleration to automatically reducethe first rotation speed LM_(RPM) and the second rotation speed RM_(RPM)by shifting a speed stage of each of the left and right traveling motors36L and 36R from a second speed to a first speed that is lower than thesecond speed. The controller 60 is configured or programmed todetermine, based on the second rotation speed RM_(RPM), the leftthresholds (that is, the first left threshold ST1 _(L) and the secondleft threshold ST2 _(L)) for judging whether to perform the automaticdeceleration in left pivot turn of the machine body 2, and to determine,based on the first rotation speed LM_(RPM), the right thresholds (thatis, the first right threshold ST1 _(R) and the second right thresholdST2 _(R)) for judging whether to perform the automatic deceleration inright pivot turn of the machine body 2.

According to the above configuration, in a case of left pivot turn, thesecond rotation speed RM_(RPM) of the right traveling motor 36R isfaster than the first rotation speed LM_(RPM) of the left travelingmotor 36L, and in right pivot turn, the first rotation speed LM_(RPM) ofthe left traveling motor 36L is faster than the second rotation speedRM_(RPM) of the right traveling motor 36R. That is, since a rotationspeed of the traveling motor opposite to a turn direction is faster, thedeceleration thresholds for automatic deceleration (that is, the leftthreshold and the right threshold) are determined based on a rotationspeed of the traveling motor to enable smooth automatic decelerationcorresponding to left pivot turn or right pivot turn. In other words,automatic deceleration can be prevented from being performedunintentionally at the time of left pivot turn or right pivot turn, andthus automatic deceleration can be performed only as necessary.

The controller 60 is configured or programmed to determine the leftthresholds (that is, the first left threshold ST1 _(L) and the secondleft threshold ST2 _(L)) to be lower as the second rotation speedRM_(RPM) decrease, to determine the left thresholds (that is, the firstleft threshold ST1 _(L) and the second left threshold ST2 _(L)) to behigher as the second rotation speed RM_(RPM) increases, to determine theright thresholds (that is, the first right threshold ST1 _(R) and thesecond right threshold ST2 _(R)) to be lower as the first rotation speedLM_(RPM) decreases, and to determine the right thresholds (that is, thefirst right threshold ST1 _(R) and the second right threshold ST2 _(R))to be higher as the first rotation speed LM_(RPM) increases. Accordingto this configuration, automatic deceleration corresponding to leftpivot turn or right pivot turn can be performed smoothly. In otherwords, it is possible to suppress unintentional automatic decelerationat the time of left pivot turn or right pivot turn, and thus automaticdeceleration can be performed only as necessary.

The working machine 1 includes the first circulation fluid line 57 hconnecting the left traveling pump 53L to the left traveling motor 36L,the second circulation fluid line 57 i connecting the right travelingpump 53R to the right traveling motor 36R, the first pressure detector80 a located on the portion of the first circulation fluid line 57 hconnected to the first port P11 of the left traveling motor 36L andconfigured to detect the first traveling pressure V1 that is thepressure of operation fluid flowing in the portion of the firstcirculation fluid line 57 h connected to the first port P11 duringrotation of the left traveling motor 36L, the second pressure detector80 b provided on the portion of the first circulation fluid line 57 hconnected to the second port P12 of the left traveling motor 36L andconfigured to detect the second traveling pressure V2 that is thepressure of operation fluid flowing in the portion of the firstcirculation fluid line 57 h connected to the second port P12 duringrotation of the left traveling motor 36L, the third pressure detector 80c provided on the portion of the second circulation fluid line 57 iconnected to the third port P13 of the right traveling motor 36R andconfigured to detect the third traveling pressure V3 that is thepressure of operation fluid flowing in the portion of the secondcirculation fluid line 57 i connected to the third port P13 duringrotation of the right traveling motor 36R, and the fourth pressuredetector 80 d provided on the portion of the second circulation fluidline 57 i connected to the fourth port P14 of the right traveling motor36R and configured to detect the fourth traveling pressure V4 that isthe pressure of operation fluid flowing in the portion of the secondcirculation fluid line 57 i connected to the fourth port P14 duringrotation of the right traveling motor 36R.

In the above-described configuration, the controller 60 is configured orprogrammed to perform the automatic deceleration during left pivot turnof the machine body 2 when the third traveling pressure V3 or the fourthtraveling pressure V4 is equal to or higher than the left threshold(that is, the first left threshold ST1 _(L)), and to perform theautomatic deceleration during right pivot turn of the machine body 2when the first traveling pressure V1 or the second traveling pressure V2is equal to or higher than the right threshold (that is, the first rightthreshold ST1 _(R)). According to this configuration, in left pivot turnof the machine body 2, automatic deceleration can be performed when thetraveling pressures (that is, the third traveling pressure V3 and thefourth traveling pressure V4) corresponding to the right traveling motor36R are equal to or higher than the left threshold (that is, the firstleft threshold ST1 _(L)). In addition, in right pivot turn of themachine body 2, automatic deceleration can be performed when thetraveling pressures (that is, the first traveling pressure V1 and thesecond traveling pressure V2) corresponding to the left traveling motor36L are equal to or higher than the left threshold (that is, the firstright threshold ST1 _(R)).

As another example, the controller 60 is configured or programmed toperform the automatic deceleration during left pivot turn of the machinebody 2 when the third differential pressure ΔV3 which is obtained bysubtracting the fourth traveling pressure V4 from the third travelingpressure V3 or the fourth differential pressure ΔV4 which is obtained bysubtracting the third traveling pressure V3 from the fourth travelingpressure V4 is equal to or higher than the left threshold (that is, thesecond left threshold ST2 _(L)), and performs the automatic decelerationduring right pivot turn of the machine body 2 when the firstdifferential pressure ΔV1 which is obtained by subtracting the secondtraveling pressure V2 from the first traveling pressure V1 or the seconddifferential pressure ΔV2 which is obtained by subtracting the firsttraveling pressure V1 from the second traveling pressure V2 is equal toor higher than the right threshold (that is, the second right thresholdST2 _(R)). According to this configuration, in left pivot turn of themachine body 2, automatic deceleration can be performed when theeffective traveling pressures (that is, the third differential pressureΔV3 and the fourth differential pressure ΔV4) corresponding to the righttraveling motor 36R are equal to or higher than the left threshold (thatis, the second left threshold ST2 _(L)). In addition, in right pivotturn of the machine body 2, automatic deceleration can be performed whenthe effective traveling pressures (that is, the first differentialpressure ΔV1 and the second differential pressure ΔV2) corresponding tothe left traveling motor 36L is equal to or higher than the leftthreshold (that is, the second right threshold ST2 _(R)).

The controller 60 is configured or programmed to change the leftthresholds (that is, the first left threshold ST1 _(L) and the secondleft threshold ST2 _(L)) and the right thresholds (that is, the firstright threshold ST1 _(R) and the second right threshold ST2 _(R))according to variation in a revolving speed of the prime mover 32.According to this configuration, the left threshold and the rightthreshold can be changed according to a revolving speed of the primemover 32, which varies depending on a load of the prime mover, so thatautomatic deceleration can be performed according to the load.

The controller 60 is configured or programmed to determine the leftthresholds (that is, the first left threshold ST1 _(L) and the secondleft threshold ST2 _(L)) for the left pivot turn of the machine body 2when the traveling operation device 54 is operated in a directioncorresponding to the left pivot turn, and to determine the rightthresholds (that is, the first right threshold ST1 _(R) and the secondright threshold ST2 _(R)) for the right pivot turn of the machine body 2when the traveling operation device 54 is operated in a directioncorresponding to the right pivot turn. According to this configuration,the left threshold and the right threshold can be determined accordingto the rotation speeds LM_(RPM) and RM_(RPM) of the traveling motors 36Land 36R immediately before pivot turn of the machine body 2, and therebyautomatic deceleration is performed.

The controller 60 is configured or programmed to determine the spin-turnthresholds (that is, the first spin-turn threshold ST1 _(P) and thesecond spin-turn threshold ST2 _(P)) for judging whether to performautomatic deceleration during spin-turn of the machine body 2, accordingto faster one of the first rotation speed LM_(RPM) and the secondrotation speed RM_(RPM). According to this configuration, when arotation difference occurs between the rotation speeds LM_(RPM) andRM_(RPM) of the traveling motors 36L and 36R in spin turn, automaticdeceleration can be performed as necessary.

The controller 60 is configured or programmed to determine the spin-turnthreshold for judging whether to perform automatic deceleration duringspin-turn of the machine body 2 so that the spin turn threshold is lowerthan the left thresholds (that is, the first left threshold ST1 _(L) andthe second left threshold ST2 _(L)) and the right thresholds (that is,the first right threshold STIR and the second right threshold ST2 _(R)).According to this configuration, automatic deceleration can be smoothlyperformed as necessary in spin turn of the machine body 2.

The controller 60 is configured or programmed to perform the automaticdeceleration during the spin turn of the machine body 2 when any one ofthe first traveling pressure V1, the second traveling pressure V2, thethird traveling pressure V3, and the fourth traveling pressure V4 isequal to or higher than the spin-turn threshold (that is, the firstspin-turn threshold ST1 _(P)). According to this configuration, it ispossible to judge whether to perform automatic deceleration at the timeof spin turn according to the first traveling pressure V1, the secondtraveling pressure V2, the third traveling pressure V3, and the fourthtraveling pressure V4, and automatic deceleration can be performed onlywhen any one of the first traveling pressure V1, the second travelingpressure V2, the third traveling pressure V3, and the fourth travelingpressure V4 is equal to or higher than the spin-turn threshold (that is,first spin-turn threshold ST1 _(P)).

In a case of spin turn of the machine body 2, the controller 60 isconfigured or programmed to perform the automatic deceleration when thetraveling operation device 54 is operated in a direction correspondingto the spin turn under a state where any one of the first travelingpressure V1, the second traveling pressure V2, the third travelingpressure V3, and the fourth traveling pressure V4 is equal to or higherthan the spin-turn threshold. According to this configuration, automaticdeceleration can be performed according to the traveling pressures V1 toV4 immediately before spin turn of the machine body 2.

The controller 60 is configured or programmed to perform the automaticdeceleration during spin turn of the machine body 2 when any one of thefirst differential pressure ΔV1 obtained by subtracting the secondtraveling pressure V2 from the first traveling pressure V1, the seconddifferential pressure ΔV2 obtained by subtracting the first travelingpressure V1 from the second traveling pressure V2, the thirddifferential pressure ΔV3 obtained by subtracting the fourth travelingpressure V4 from the third traveling pressure V3, and the fourthdifferential pressure ΔV4 obtained by subtracting the third travelingpressure V3 from the fourth traveling pressure V4 is equal to or higherthan the spin-turn threshold (that is, the second spin-turn thresholdST2 _(P)). According to this configuration, it is possible to judgewhether to perform automatic deceleration in spin turn according to thefirst differential pressure ΔV1, second differential pressure ΔV2, thirddifferential pressure ΔV3, and fourth differential pressure ΔV4, and itis possible to perform automatic deceleration only when one of the firstdifferential pressure ΔV1, second differential pressure ΔV2, thirddifferential pressure ΔV3, and fourth differential pressure ΔV4 is equalto or higher than the spin-turn threshold (that is, the second spin-turnthreshold ST2 _(P)).

The controller 60 is configured or programmed to determine thestraight-traveling thresholds (that is, the first straight-travelingthreshold SF1 _(S) and the second straight-traveling threshold SF2 _(S))for determining whether to perform automatic deceleration in straighttraveling of the machine body 2, based on the rotation difference ΔMPbetween the first rotation speed LM_(RPM) and the second rotation speedRM_(RPM) or the rotation-ratio difference ΔDP. For example, when themachine body 2 shifts from a state of pivot turn to a state of straighttraveling, there will be a difference between the first rotation speedLM_(RPM) of the left traveling motor 36L and the second rotation speedRM_(RPM) of the right traveling motor 36R. In such a case, a travelingspeed of the machine body 2 can be kept by determining the straighttraveling thresholds (that is, first straight traveling threshold SF1_(S) and the second straight traveling threshold SF2 _(S)) based on therotation difference ΔMP between the first rotation speed LM_(RPM) andthe second rotation speed RM_(RPM) or rotation-ratio difference ΔDP.That is, when the machine body 2 shifts from a state of pivot turn to astraight of straight traveling, automatic deceleration is not performed,and when straight traveling of the machine body 2 becomes stable,automatic deceleration can be performed as necessary.

The controller 60 is configured or programmed to determine thestraight-traveling thresholds (that is, the first straight-travelingthreshold SF1 _(S) and the second straight-traveling threshold SF2 _(S))to be higher as the rotation difference ΔMP increases, and determinesthe straight-traveling thresholds (that is, the first straight-travelingthreshold SF1 _(S) and the second straight-traveling threshold SF2 _(S))to be lower as the rotation difference ΔMP decreases. This makes itdifficult to perform automatic deceleration when a state of the machinebody 2 is close to a state of pivot turn (that is, when the rotationdifference ΔMP is large), and makes it easy to perform automaticdeceleration when the state is close to a state of straight traveling(that is, when the rotation difference ΔMP is small).

The controller 60 is configured or programmed to determine thestraight-traveling thresholds (that is, the first straight-travelingthreshold SF1 _(S) and the second straight-traveling threshold SF2 _(S))to be higher as the rotation-ratio difference ΔDP increases, anddetermines the straight-traveling thresholds (that is, the firststraight-traveling threshold SF1 _(S) and the second straight-travelingthreshold SF2 _(S)) to be lower as the rotation-ratio difference ΔDPdecreases. This makes it difficult to perform automatic decelerationwhen a state of the machine body 2 is close to a state of pivot turn(that is, when the rotation-ratio difference ΔDP is large), and makes iteasy to perform automatic deceleration when the state is close to astate of straight traveling (that is, when the rotation-ratio differenceΔDP is small).

The controller 60 is configured or programmed to perform the automaticdeceleration during forward straight traveling of the machine body 2when either the first traveling pressure V1 or the third travelingpressure V3 is the straight-traveling threshold (that is, the firststraight-traveling threshold SF1 _(S)). According to this configuration,when the machine body 2 travels forward, automatic deceleration can beperformed based on the traveling pressure corresponding to the lefttraveling motor 36L (that is, the first traveling pressure V1) and thetraveling pressure corresponding to the right traveling motor 36R (thatis, third traveling pressure V3).

The controller 60 is configured or programmed to perform the automaticdeceleration during forward straight traveling of the machine body 2when either the first differential pressure ΔV1 obtained by subtractingthe second traveling pressure V2 from the first traveling pressure V1 orthe third differential pressure ΔV3 obtained by subtracting the fourthtraveling pressure V4 from the third traveling pressure V3 is equal toor higher than the straight-traveling threshold (that is, the secondstraight-traveling threshold SF2 _(S)). According to this configuration,when the machine body 2 travels forward, automatic deceleration can beperformed based on the effective differential pressure corresponding tothe left traveling motor 36L (that is, the first differential pressureΔV1) and the effective differential pressure corresponding to the righttraveling motor 36R (that is, the third differential pressure ΔV3).

The controller 60 is configured or programmed to determine thestraight-traveling thresholds (that is, the first straight-travelingthreshold SF1 _(S) and the second straight-traveling threshold SF2 _(S))based on the first rotation speed LM_(RPM) detected by the firstrotation detector 68 a and the second rotation speed RM_(RPM) detectedby the second rotation detector 68 b. For example, when a vehicle speedof the machine body 2 is increased from a low speed, or when the machinebody 2 is accelerated from a stopping state, the first rotation speedLM_(RPM) of the left traveling motor 36L and the second rotation speedRM_(RPM) of the right traveling motor 36R increase (become higher). Insuch cases, automatic deceleration can be performed when straighttraveling of the machine body 2 becomes stable, while preventingautomatic deceleration from being performed.

The controller 60 is configured or programmed to determine thestraight-traveling thresholds (that is, the first straight-travelingthreshold SF1 _(S) and the second straight-traveling threshold SF2 _(S))to be lower when the first rotation speed LM_(RPM) or the secondrotation speed RM_(RPM) is low, and to determine the straight-travelingthresholds (that is, the first straight-traveling threshold SF1 _(S) andthe second straight-traveling threshold SF2 _(S)) to be higher when thefirst rotation speed LM_(RPM) or the second rotation speed RM_(RPM) ishigh. According to this configuration, when a vehicle speed of themachine body 2 is increased from a low speed or when the machine body 2is accelerated from a stopping state, automatic deceleration issuppressed, while the automatic deceleration can be performed whenstraight traveling of the machine body 2 becomes stable.

The controller 60 is configured or programmed to perform the automaticdeceleration during forward straight traveling of the machine body 2when a time for which both the first traveling pressure V1 and the thirdtraveling pressure V3 are equal to or higher than the straight-travelingthreshold (that is, the first straight-traveling threshold SF1 _(S)) isequal to or longer than a first judgment time. This allows automaticdeceleration to be performed when a time elapsed when the travelingpressure corresponding to the left traveling motor 36L (that is, thefirst traveling pressure V1) and the traveling pressure corresponding tothe right traveling motor 36R (that is, the third traveling pressure V3)are equal to or higher than the straight traveling threshold (that is,the first straight traveling threshold SF1 _(S)) is equal to or longerthan the first judgment time in forward traveling of the machine body 2.That is, automatic deceleration can be performed when the firsttraveling pressure V1 and the third traveling pressure V3 are equal toor higher than the straight traveling threshold (that is, the firststraight traveling threshold SF1 _(S)) for a certain period of time.

The controller 60 is configured or programmed to determine the firstjudgment time to be shorter as the first rotation speed LM_(RPM) or thesecond rotation speed RM_(RPM) increases, and determines the firstjudgment time to be longer as the first rotation speed LM_(RPM) or thesecond rotation speed RM_(RPM) decreases. According to thisconfiguration, when the first rotation speed LM_(RPM) or the secondrotation speed RM_(RPM) is small and a vehicle speed (that is, atraveling speed) is slow (that is, low), the first judgment time becomeslonger, so that automatic deceleration can be performed only when thevehicle speed is slow for a long time. On the other hand, when the firstrotation speed LM_(RPM) or the second rotation speed RM_(RPM) is largeand the vehicle speed (that is, the traveling speed) is high, automaticdeceleration can be performed quickly as necessary.

The controller 60 is configured or programmed to perform the automaticdeceleration during forward straight traveling of the machine 2 when atime for which both the first differential pressure ΔV1 obtained bysubtracting the second traveling pressure V2 from the first travelingpressure V1 and the third differential pressure ΔV3 obtained bysubtracting the fourth traveling pressure V4 from the third travelingpressure V3 is equal to or higher than the straight-traveling threshold(that is, the second straight-traveling threshold SF2 _(S)) is equal toor longer than the second judgment time. According to thisconfiguration, when the machine body 2 moves forward, and when a timeelapsed when the effective traveling pressure corresponding to the lefttraveling motor 36L (that is, the first differential pressure ΔV1) andthe effective traveling pressure corresponding to the right travelingmotor 36R (that is, the differential pressure ΔV3) are equal to orhigher than the straight traveling threshold (that is, the secondstraight traveling threshold SF2 _(S)) is equal to or longer than thesecond judgment time in forward traveling, automatic deceleration can beperformed. That is, automatic deceleration can be performed when theeffective traveling pressure (that is, the first differential pressureΔV1) and the effective traveling pressure (that is, the thirddifferential pressure ΔV3) are equal to or higher than the straighttraveling threshold (that is, the second straight traveling thresholdSF2 _(S)) for a certain period of time.

The controller 60 is configured or programmed to determine the secondjudgment time to be shorter as the first rotation speed LM_(RPM) or thesecond rotation speed RM_(RPM) increases, and to determine the secondjudgment time to be longer as the first rotation speed LM_(RPM) or thesecond rotation speed RM_(RPM) decreases. According to thisconfiguration, when the first rotation speed LM_(RPM) or the secondrotation speed RM_(RPM) is small and a vehicle speed (that is, atraveling speed) is slow, the first judgment time becomes longer, sothat automatic deceleration can be performed only when the vehicle speedis slow for a long time. On the other hand, when the first rotationspeed LM_(RPM) or the second rotation speed RM_(RPM) is large and thevehicle speed (that is, the traveling speed) is fast (that is, high),automatic deceleration can be performed quickly as necessary.

The controller 60 is configured or programmed so that it does notperform the automatic deceleration when the traveling operation member59 is operated in a direction to make the machine body 2 travel forwardand the left traveling motor 36L and the right traveling motor 36R arerotating in a direction corresponding to backward traveling of themachine body 2. According to this configuration, when the travelingoperation member 59 is instantaneously operated in a forward-travelingdirection from the state in which the machine body 2 is travelingbackward, automatic deceleration is not performed, thereby stabilizingthe backward traveling of the working machine 1.

The controller 60 is configured or programmed so that it does notperform the automatic deceleration when the first rotation speedLM_(RPM) of the left traveling motor 36L is equal to or higher than apredetermined rotation speed or the second rotation speed RM_(RPM) ofthe right traveling motor 36R is equal to or higher than thepredetermined rotation speed. According to this configuration,workability can be improved by not performing automatic decelerationwhen the first rotation speed LM_(RPM) and the second rotation speedRM_(RPM) are high.

The controller 60 is configured or programmed so that it does notperform the automatic deceleration when the first rotation speedLM_(RPM) of the left traveling motor 36L is equal to or higher than thefirst maximum rotation speed or when the second rotation speed RM_(RPM)of the right traveling motor 36R is equal to or higher than the secondmaximum rotation speed. For example, even when a rotation speed of theleft traveling motor 36L exceeds the first maximum rotation speed of theleft traveling motor 36L at the first speed or a rotation speed of theright traveling motor 36R exceeds the second maximum rotation speed ofthe right traveling motor 36R at the first speed in a state where themachine body 2 is climbing a hill at the second speed, automaticdeceleration is not performed, thereby allowing the machine body 2 totravel without deteriorating a traveling performance.

In the above-mentioned embodiment, the left traveling motor 36L and theright traveling motor 36R are configured to simultaneously switch theirspeed stages to the first speed or the second speed, and automaticdeceleration is also performed simultaneously to the left travelingmotor 36L and the right traveling motor 36R; the automatic decelerationmay be performed with at least one of the left traveling motor 36L andthe right traveling motor 36R switched to the first speed or to thesecond speed and with at least one of the left traveling motor 36L andthe right traveling motor 36R being at the second speed. Furthermore,the switchable speed stages of the left traveling motor 36L and theright traveling motor 36R may not be limited to two, but be three ormore.

The traveling motors 36L and 36R may be axial piston motors or radialpiston motors. Regardless of whether the traveling motors 36L and 36Rare radial piston motors or radial piston motors, when a pressure ofoperation fluid supplied to the motors becomes high, rotation speeds ofthe traveling motors can be switched to the first speed, and when thepressure of operation fluid supplied to the motors becomes low, therotation speeds of the traveling motors can be switched to the secondspeed.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A working machine comprising: a machine body; aleft traveling device located left on the machine body; a righttraveling device located right on the machine body; a left travelingmotor to output a power to the left traveling device; a right travelingmotor to output a power to the right traveling device; a first rotationdetector to detect a first rotation speed that is a rotation speed ofthe left traveling motor; a second rotation detector to detect a secondrotation speed that is a rotation speed of the right traveling motor; aleft traveling pump to supply operation fluid to the left travelingmotor; a right traveling pump to supply operation fluid to the righttraveling motor; a traveling operation device to operate at least one ofthe left traveling pump and the right traveling pump; and a controllerconfigured or programmed to perform automatic deceleration toautomatically reduce the first rotation speed and the second rotationspeed by shifting a speed stage of each of the left and right travelingmotors from a second speed stage to a first speed stage that is lowerthan the second speed, wherein the controller is configured orprogrammed to determine, based on the second rotation speed, a leftthreshold for judging whether to perform the automatic deceleration inleft pivot turn of the machine body, and to determine, based on thefirst rotation speed, a right threshold for judging whether to performthe automatic deceleration in right pivot turn of the machine body. 2.The working machine according to claim 1, wherein the controller isconfigured or programmed: to determine the left threshold to be lower asthe second rotation speed decrease, to determine the left threshold tobe higher as the second rotation speed increases, to determine the rightthreshold to be lower as the first rotation speed decreases, and todetermine the right threshold to be higher as the first rotation speedincreases.
 3. The working machine according to claim 1, comprising: afirst circulation fluid line connecting the left traveling pump to theleft traveling motor; a second circulation fluid line connecting theright traveling pump to the right traveling motor; a first pressuredetector provided on a portion of the first circulation fluid lineconnected to a first port of the left traveling motor and configured todetect a first traveling pressure that is a pressure of operation fluidflowing in the portion of the first circulation fluid line connected tothe first port during rotation of the left traveling motor; a secondpressure detector provided on a portion of the first circulation fluidline connected to a second port of the left traveling motor andconfigured to detect a second traveling pressure that is a pressure ofoperation fluid flowing in the portion of the first circulation fluidline connected to the second port during rotation of the left travelingmotor; a third pressure detector provided on a portion of the secondcirculation fluid line connected to a third port of the right travelingmotor and configured to detect a third traveling pressure that is apressure of operation fluid flowing in the portion of the secondcirculation fluid line connected to the third port during rotation ofthe right traveling motor; and a fourth pressure detector provided on aportion of the second circulation fluid line connected to a fourth portof the right traveling motor and configured to detect a fourth travelingpressure that is a pressure of operation fluid flowing in the portion ofthe second circulation fluid line connected to the fourth port duringrotation of the right traveling motor, wherein the controller isconfigured or programmed to perform the automatic deceleration duringleft pivot turn of the machine body when the third traveling pressure orthe fourth traveling pressure is equal to or higher than the leftthreshold; and to perform the automatic deceleration during right pivotturn of the machine body when the first traveling pressure or the secondtraveling pressure is equal to or higher than the right threshold. 4.The working machine according to claim 2, comprising: a firstcirculation fluid line connecting the left traveling pump to the lefttraveling motor; a second circulation fluid line connecting the righttraveling pump to the right traveling motor; a first pressure detectorprovided on a portion of the first circulation fluid line connected to afirst port of the left traveling motor and configured to detect a firsttraveling pressure that is a pressure of operation fluid flowing in theportion of the first circulation fluid line connected to the first portduring rotation of the left traveling motor; a second pressure detectorprovided on a portion of the first circulation fluid line connected to asecond port of the left traveling motor and configured to detect asecond traveling pressure that is a pressure of operation fluid flowingin the portion of the first circulation fluid line connected to thesecond port during rotation of the left traveling motor; a thirdpressure detector provided on a portion of the second circulation fluidline connected to a third port of the right traveling motor andconfigured to detect a third traveling pressure that is a pressure ofoperation fluid flowing in the portion of the second circulation fluidline connected to the third port during rotation of the right travelingmotor; and a fourth pressure detector provided on a portion of thesecond circulation fluid line connected to a fourth port of the righttraveling motor and configured to detect a fourth traveling pressurethat is a pressure of operation fluid flowing in the portion of thesecond circulation fluid line connected to the fourth port duringrotation of the right traveling motor, wherein the controller isconfigured or programmed to perform the automatic deceleration duringleft pivot turn of the machine body when the third traveling pressure orthe fourth traveling pressure is equal to or higher than the leftthreshold; and to perform the automatic deceleration during right pivotturn of the machine body when the first traveling pressure or the secondtraveling pressure is equal to or higher than the right threshold. 5.The working machine according to claim 1, comprising: a firstcirculation fluid line connecting the left traveling pump to the lefttraveling motor; a second circulation fluid line connecting the righttraveling pump to the right traveling motor; a first pressure detectorprovided on a portion of the first circulation fluid line connected to afirst port of the left traveling motor and configured to detect a firsttraveling pressure that is a pressure of operation fluid flowing in theportion of the first circulation fluid line connected to the first portduring rotation of the left traveling motor; a second pressure detectorprovided on a portion of the first circulation fluid line connected to asecond port of the left traveling motor and configured to detect asecond traveling pressure that is a pressure of operation fluid flowingin the portion of the first circulation fluid line connected to thesecond port during rotation of the left traveling motor; a thirdpressure detector provided on a portion of the second circulation fluidline connected to a third port of the right traveling motor andconfigured to detect a third traveling pressure that is a pressure ofoperation fluid flowing in the portion of the second circulation fluidline connected to the third port during rotation of the right travelingmotor; and a fourth pressure detector provided on a portion of thesecond circulation fluid line connected to a fourth port of the righttraveling motor and configured to detect a fourth traveling pressurethat is a pressure of operation fluid flowing in the portion of thesecond circulation fluid line connected to the fourth port duringrotation of the right traveling motor, wherein the controller isconfigured or programmed to perform the automatic deceleration duringleft pivot turn of the machine body when a third differential pressureobtained by subtracting the fourth traveling pressure from the thirdtraveling pressure or a fourth differential pressure obtained bysubtracting the third traveling pressure from the fourth travelingpressure is equal to or higher than the left threshold, and to performthe automatic deceleration during right pivot turn of the machine bodywhen a first differential pressure obtained by subtracting the secondtraveling pressure from the first traveling pressure or a seconddifferential pressure obtained by subtracting the first travelingpressure from the second traveling pressure is equal to or higher thanthe right threshold.
 6. The working machine according to claim 2,comprising: a first circulation fluid line connecting the left travelingpump to the left traveling motor; a second circulation fluid lineconnecting the right traveling pump to the right traveling motor; afirst pressure detector provided on a portion of the first circulationfluid line connected to a first port of the left traveling motor andconfigured to detect a first traveling pressure that is a pressure ofoperation fluid flowing in the portion of the first circulation fluidline connected to the first port during rotation of the left travelingmotor; a second pressure detector provided on a portion of the firstcirculation fluid line connected to a second port of the left travelingmotor and configured to detect a second traveling pressure that is apressure of operation fluid flowing in the portion of the firstcirculation fluid line connected to the second port during rotation ofthe left traveling motor; a third pressure detector provided on aportion of the second circulation fluid line connected to a third portof the right traveling motor and configured to detect a third travelingpressure that is a pressure of operation fluid flowing in the portion ofthe second circulation fluid line connected to the third port duringrotation of the right traveling motor; and a fourth pressure detectorprovided on a portion of the second circulation fluid line connected toa fourth port of the right traveling motor and configured to detect afourth traveling pressure that is a pressure of operation fluid flowingin the portion of the second circulation fluid line connected to thefourth port during rotation of the right traveling motor, wherein thecontroller is configured or programmed to perform the automaticdeceleration during left pivot turn of the machine body when a thirddifferential pressure obtained by subtracting the fourth travelingpressure from the third traveling pressure or a fourth differentialpressure obtained by subtracting the third traveling pressure from thefourth traveling pressure is equal to or higher than the left threshold,and to perform the automatic deceleration during right pivot turn of themachine body when a first differential pressure obtained by subtractingthe second traveling pressure from the first traveling pressure or asecond differential pressure obtained by subtracting the first travelingpressure from the second traveling pressure is equal to or higher thanthe right threshold.
 7. The working machine according to claim 1,wherein the controller is configured or programmed to change the leftthreshold and the right threshold according to variation in a revolvingspeed of a prime mover.
 8. The working machine according to claim 1,wherein the controller is configured or programmed: to determine theleft threshold when the traveling operation device is operated in adirection corresponding to the left pivot turn of the machine body, andto determine the right threshold when the traveling operation device isoperated in a direction corresponding to the right pivot turn of themachine body.
 9. The working machine according to claim 2, wherein thecontroller is configured or programmed: to determine the left thresholdwhen the traveling operation device is operated in a directioncorresponding to the left pivot turn of the machine body, and todetermine the right threshold when the traveling operation device isoperated in a direction corresponding to the right pivot turn of themachine body.
 10. The working machine according to claim 3, wherein thecontroller is configured or programmed: to determine the left thresholdwhen the traveling operation device is operated in a directioncorresponding to the left pivot turn of the machine body, and todetermine the right threshold when the traveling operation device isoperated in a direction corresponding to the right pivot turn of themachine body.
 11. The working machine according to claim 4, wherein thecontroller is configured or programmed: to determine the left thresholdwhen the traveling operation device is operated in a directioncorresponding to the left pivot turn of the machine body, and todetermine the right threshold when the traveling operation device isoperated in a direction corresponding to the right pivot turn of themachine body.
 12. The working machine according to claim 5, wherein thecontroller is configured or programmed: to determine the left thresholdwhen the traveling operation device is operated in a directioncorresponding to the left pivot turn of the machine body, and todetermine the right threshold when the traveling operation device isoperated in a direction corresponding to the right pivot turn of themachine body.
 13. The working machine according to claim 6, wherein thecontroller is configured or programmed: to determine the left thresholdwhen the traveling operation device is operated in a directioncorresponding to the left pivot turn of the machine body, and todetermine the right threshold when the traveling operation device isoperated in a direction corresponding to the right pivot turn of themachine body.
 14. The working machine according to claim 1, wherein thecontroller is configured or programmed to determine, according to afaster one of the first rotation speed and the second rotation speed, aspin-turn threshold for judging whether to perform the automaticdeceleration during spin turn of the machine body.
 15. The workingmachine according to claim 1, wherein the controller is configured orprogrammed to determine a spin-turn threshold for judging whether toperform the automatic deceleration during spin turn of the machine bodyso that the spin turn threshold is lower than the left threshold and theright threshold.
 16. The working machine according to claim 14,comprising: a first circulation fluid line connecting the left travelingpump to the left traveling motor; a second circulation fluid lineconnecting the right traveling pump to the right traveling motor; afirst pressure detector provided on a portion of the first circulationfluid line connected to a first port of the left traveling motor andconfigured to detect a first traveling pressure that is a pressure ofoperation fluid flowing in the portion of the first circulation fluidline connected to the first port during rotation of the left travelingmotor; a second pressure detector provided on a portion of the firstcirculation fluid line connected to a second port of the left travelingmotor and configured to detect a second traveling pressure that is apressure of operation fluid flowing in the portion of the firstcirculation fluid line connected to the second port during rotation ofthe left traveling motor; a third pressure detector provided on aportion of the second circulation fluid line connected to a third portof the right traveling motor and configured to detect a third travelingpressure that is a pressure of operation fluid flowing in the portion ofthe second circulation fluid line connected to the third port duringrotation of the right traveling motor; and a fourth pressure detectorprovided on a portion of the second circulation fluid line connected toa fourth port of the right traveling motor and configured to detect afourth traveling pressure that is a pressure of operation fluid flowingin the portion of the second circulation fluid line connected to thefourth port during rotation of the right traveling motor, wherein thecontroller is configured or programmed to perform the automaticdeceleration during spin turn of the machine body when any one of thefirst traveling pressure, the second traveling pressure, the thirdtraveling pressure, and the fourth traveling pressure is equal to orhigher than the spin-turn threshold.
 17. The working machine accordingto claim 15, comprising: a first circulation fluid line connecting theleft traveling pump to the left traveling motor; a second circulationfluid line connecting the right traveling pump to the right travelingmotor; a first pressure detector provided on a portion of the firstcirculation fluid line connected to a first port of the left travelingmotor and configured to detect a first traveling pressure that is apressure of operation fluid flowing in the portion of the firstcirculation fluid line connected to the first port during rotation ofthe left traveling motor; a second pressure detector provided on aportion of the first circulation fluid line connected to a second portof the left traveling motor and configured to detect a second travelingpressure that is a pressure of operation fluid flowing in the portion ofthe first circulation fluid line connected to the second port duringrotation of the left traveling motor; a third pressure detector providedon a portion of the second circulation fluid line connected to a thirdport of the right traveling motor and configured to detect a thirdtraveling pressure that is a pressure of operation fluid flowing in theportion of the second circulation fluid line connected to the third portduring rotation of the right traveling motor; and a fourth pressuredetector provided on a portion of the second circulation fluid lineconnected to a fourth port of the right traveling motor and configuredto detect a fourth traveling pressure that is a pressure of operationfluid flowing in the portion of the second circulation fluid lineconnected to the fourth port during rotation of the right travelingmotor, wherein the controller is configured or programmed to perform theautomatic deceleration during spin turn of the machine body when any oneof the first traveling pressure, the second traveling pressure, thethird traveling pressure, and the fourth traveling pressure is equal toor higher than the spin-turn threshold.
 18. The working machineaccording to claim 16, wherein the controller is configured orprogrammed to perform the automatic deceleration when the travelingoperation device is operated in a direction corresponding to spin turnand any one of the first traveling pressure, the second travelingpressure, the third traveling pressure, and the fourth travelingpressure is equal to or higher than the spin-turn threshold.
 19. Theworking machine according to claim 14, comprising: a first circulationfluid line connecting the left traveling pump to the left travelingmotor; a second circulation fluid line connecting the right travelingpump to the right traveling motor; a first pressure detector provided ona portion of the first circulation fluid line connected to a first portof the left traveling motor and configured to detect a first travelingpressure that is a pressure of operation fluid flowing in the portion ofthe first circulation fluid line connected to the first port duringrotation of the left traveling motor; a second pressure detectorprovided on a portion of the first circulation fluid line connected to asecond port of the left traveling motor and configured to detect asecond traveling pressure that is a pressure of operation fluid flowingin the portion of the first circulation fluid line connected to thesecond port during rotation of the left traveling motor; a thirdpressure detector provided on a portion of the second circulation fluidline connected to a third port of the right traveling motor andconfigured to detect a third traveling pressure that is a pressure ofoperation fluid flowing in the portion of the second circulation fluidline connected to the third port during rotation of the right travelingmotor; and a fourth pressure detector provided on a portion of thesecond circulation fluid line connected to a fourth port of the righttraveling motor and configured to detect a fourth traveling pressurethat is a pressure of operation fluid flowing in the portion of thesecond circulation fluid line connected to the fourth port duringrotation of the right traveling motor, wherein the controller isconfigured or programmed to perform the automatic deceleration duringspin turn of the machine body when an one of a first differentialpressure obtained by subtracting the second traveling pressure from thefirst traveling pressure, a second differential pressure obtained bysubtracting the first traveling pressure from the second travelingpressure, a third differential pressure obtained by subtracting thefourth traveling pressure from the third traveling pressure, and afourth differential pressure obtained by subtracting the third travelingpressure from the fourth traveling pressure is equal to or higher thanthe spin-turn threshold.
 20. The working machine according to claim 15,comprising: a first circulation fluid line connecting the left travelingpump to the left traveling motor; a second circulation fluid lineconnecting the right traveling pump to the right traveling motor; afirst pressure detector provided on a portion of the first circulationfluid line connected to a first port of the left traveling motor andconfigured to detect a first traveling pressure that is a pressure ofoperation fluid flowing in the portion of the first circulation fluidline connected to the first port during rotation of the left travelingmotor; a second pressure detector provided on a portion of the firstcirculation fluid line connected to a second port of the left travelingmotor and configured to detect a second traveling pressure that is apressure of operation fluid flowing in the portion of the firstcirculation fluid line connected to the second port during rotation ofthe left traveling motor; a third pressure detector provided on aportion of the second circulation fluid line connected to a third portof the right traveling motor and configured to detect a third travelingpressure that is a pressure of operation fluid flowing in the portion ofthe second circulation fluid line connected to the third port duringrotation of the right traveling motor; and a fourth pressure detectorprovided on a portion of the second circulation fluid line connected toa fourth port of the right traveling motor and configured to detect afourth traveling pressure that is a pressure of operation fluid flowingin the portion of the second circulation fluid line connected to thefourth port during rotation of the right traveling motor, wherein thecontroller is configured or programmed to perform the automaticdeceleration during spin turn of the machine body when an one of a firstdifferential pressure obtained by subtracting the second travelingpressure from the first traveling pressure, a second differentialpressure obtained by subtracting the first traveling pressure from thesecond traveling pressure, a third differential pressure obtained bysubtracting the fourth traveling pressure from the third travelingpressure, and a fourth differential pressure obtained by subtracting thethird traveling pressure from the fourth traveling pressure is equal toor higher than the spin-turn threshold.